Dirac solitons and topological edge states in the β-Fermi-Pasta-Ulam-Tsingou dimer lattice

We consider a dimer lattice of the Fermi-Pasta-Ulam-Tsingou (FPUT) type, where alternating linear couplings have a controllably small difference and the cubic nonlinearity (β-FPUT) is the same for all interaction pairs. We use a weakly nonlinear formal reduction within the lattice band gap to obtain a continuum, nonlinear Dirac-type system. We derive the Dirac soliton profiles and the model's conservation laws analytically. We then examine the cases of the semi-infinite and the finite domains and illustrate how the soliton solutions of the bulk problem can be glued to the boundaries for different types of boundary conditions. We thus explain the existence of various kinds of nonlinear edge states in the system, of which only one leads to the standard topological edge states observed in the linear limit. We finally examine the stability of bulk and edge states and verify them through direct numerical simulations, in which we observe a solitonlike wave setting into motion due to the instability.

Strain topological metamaterials and revealing hidden topology in higher-order coordinates

Topological physics has revolutionized materials science, introducing topological phases of matter in diverse settings ranging from quantum to photonic and phononic systems. Herein, we present a family of topological systems, which we term "strain topological metamaterials", whose topological properties are hidden and unveiled only under higher-order (strain) coordinate transformations. We firstly show that the canonical mass dimer, a model that can describe various settings such as electrical circuits and optics, among others, belongs to this family where strain coordinates reveal a topological nontriviality for the edge states at free boundaries. Subsequently, we introduce a mechanical analog of the Majorana-supporting Kitaev chain, which supports topological edge states for both fixed and free boundaries within the proposed framework. Thus, our findings not only extend the way topological edge states are identified, but also promote the fabrication of novel topological metamaterials in various fields, with more complex, tailored boundaries.

Alexithymic characteristics and interoceptive abilities are associated with disease severity and levels of C-reactive protein and cytokines in patients with inflammatory bowel disease

Background

Alexithymia and atypical gut-brain signaling have been linked to the pathophysiology of inflammatory bowel disease (IBD). We herein assessed IBD patients' alexithymia levels and interoceptive abilities, and detected potential correlations with psychological distress, symptom severity and disease activity, and inflammation indices.

Methods

Adult IBD outpatients and healthy controls were recruited. Alexithymia was assessed using the Toronto Alexithymia Scale, interoceptive accuracy using the Heartbeat Counting Test (cardiac interoception) and the Water Load Test-II (gastric interoception), and interoceptive sensibility using the Multidimensional Assessment of Interoceptive Awareness (MAIA).

Results

Forty-one patients with Crohn's disease (CD), 16 with ulcerative colitis (UC), and 50 healthy controls were included. In CD patients, the level of externally oriented thinking and total alexithymia score were correlated with disease activity (P=0.027 and P=0.047, respectively), while in UC patients difficulties in identifying emotions were linked to disease activity (P=0.007). In CD patients, the Noticing, Not-Worrying and Emotional Awareness MAIA subscale score were correlated with C-reactive protein levels (P=0.005, P=0.048 and P=0.005), the Noticing subscale score with interleukin (IL)-1β levels (r=-0.350, P=0.039), the Not-Distracting subscale score with IL-6 levels (r=-0.402, P=0.017), and the Emotional Awareness subscale score with IL-1β (r=-0.367, P=0.030) and IL-6 (r=-0.379, P=0.025) levels. Finally, in UC patients, the Not-Worrying subscale score was significantly associated with IL-6 levels (r=-0.532, P=0.049), while difficulties in identifying emotions were linked to IL-8 levels (r=0.604, P=0.022).

Conclusion

Emotional and interoceptive processing is associated with IBD disease activity, suggesting a potential implication for IBD pathophysiology.

Modulation instability in nonlinear flexible mechanical metamaterials

In this paper, we study modulation instabilities (MI) in a one-dimensional chain configuration of a flexible mechanical metamaterial (flexMM). Using the lumped element approach, flexMMs can be modeled by a coupled system of discrete equations for the longitudinal displacements and rotations of the rigid mass units. In the long wavelength regime, and applying the multiple-scales method we derive an effective nonlinear Schrödinger equation for slowly varying envelope rotational waves. We are then able to establish a map of the occurrence of MI to the parameters of the metamaterials and the wave numbers. We also highlight the key role of the rotation-displacement coupling between the two degrees of freedom in the manifestation of MI. All analytical findings are confirmed by numerical simulations of the full discrete and nonlinear lump problem. These results provide interesting design guidelines for nonlinear metamaterials offering either stability to high amplitude waves, or conversely being good candidates to observe instabilities.

The Inflammatory Bowel Disease-Disk Tool for Assessing Disability in Inflammatory Bowel Disease Patients: Validation of the Greek Version

BACKGROUND

The Inflammatory Bowel Disease-Disk (IBD-Disk) is a physician-administered tool that evaluates the functional status of patients with Inflammatory Bowel Disease (IBD). The aim of our study was to validate the content of the IBD-Disk in a Greek cohort of IBD patients.

METHODS

Two questionnaires [the IBD Disk and the IBD-Disability Index (IBD-DI)] were translated into Greek and administered to IBD patients at baseline visit, after 4 weeks and 6 months. Validation of the IBD Disk included measuring of concurrent validity, reproducibility, and internal consistency.

RESULTS

A total of 300 patients were included at baseline and 269 at follow-up. There was a good correlation between the total scores of the IBD-Disk and IBD-DI at baseline (Pearson correlation 0.87, p < 0.001). Reproducibility of the total IBD-Disk score was very good [intra-class correlation coefficient (ICC), 95% confidence interval (CI) 0.89 (0.86-0.91)]. Cronbach's coefficient alpha for all items achieved 0.90 (95%CI 0.88-0.92), demonstrating a very good homogeneity of the IBD-Disk items. Female gender and extraintestinal manifestations were significantly associated with a higher IBD-Disk total score.

CONCLUSIONS

The Greek version of the IBD-Disk proved to be a reliable and valid tool in detecting and assessing IBD-related disability in a Greek cohort of IBD patients.

The natural history of COVID-19 in vaccinated inflammatory bowel disease patients

AIM

Assess the characteristics of break through COVID-19 in Inflammatory Bowel Disease (IBD) patients, despite complete vaccination.

METHODS

Patients who reported a COVID-19 at least 3 weeks after complete vaccination were asked to answer an on-line anonymous questionnaire which included patient and disease characteristics, vaccination history, and the evolution of COVID-19.

RESULTS

Among 3240 IBD patients who reported complete vaccination between 1st May 2021 and 30thJune 2022, 402 (12.4%) were infected by SARS Cov-2 [223 male, 216 Crohn's disease (CD), 186 Ulcerative Colitis (UC), mean (SD) age 42.3 (14.9) years, mean (SD) IBD duration 10.1 (9.7) years]. Three hundred and sixty-nine patients (91.8%) were infected once and 33 (8.2%) twice. The mean (SD) time between last vaccination and infection was 4.1 (1.6) months. Overall, 351 (87.3%) patients reported mild constitutional and/or respiratory symptoms, 34 (8.4%) were asymptomatic and only 17 patients (4.2%) required hospitalization. Of hospitalized patients, 2 UC patients died of COVID-19 pneumonia. The remaining hospitalized patients did not need high flow oxygen supply or ICU admission.

CONCLUSIONS

A minority of completely vaccinated IBD patients developed COVID-19 which evolved with mild symptoms and a favorable outcome. These results reinforce the importance of vaccination especially in vulnerable populations.

Subwavelength Su-Schrieffer-Heeger topological modes in acoustic waveguides

Topological systems furnish a powerful way of localizing wave energy at edges of a structured material. Usually, this relies on Bragg scattering to obtain bandgaps with nontrivial topological structures. However, this limits their applicability to low frequencies because that would require very large structures. A standard approach to address the problem is to add resonating elements inside the material to open gaps in the subwavelength regime. Unfortunately, generally, one has no precise control on the properties of the obtained topological modes, such as their frequency or localization length. In this work, a unique construction is proposed to couple acoustic resonators such that acoustic modes are mapped exactly to the eigenmodes of the Su-Schrieffer-Heeger (SSH) model. The relation between energy in the lattice model and the acoustic frequency is controlled by the characteristics of the resonators. In this way, SSH topological modes are obtained at any given frequency, for instance, in the subwavelength regime. The construction is also generalized to obtain well-controlled topological edge modes in alternative tunable configurations.

Acute Upper Gastrointestinal Bleeding: Less Severe Bleeding in More Frail and Older Patients, Comparison Between Two Time Periods Fifteen Years Apart

Background

Acute upper gastrointestinal bleeding (AUGIB) remains a common medical emergency with considerable morbidity and mortality. The aim of this study was to describe the patient characteristics, diagnoses and clinical outcomes of patients presenting with AUGIB nowadays and compare these with those of patients 15 years ago.

Methods

This was a single-center survey of adults (> 16 years) presenting with AUGIB to a tertiary hospital. Data from 401 patients presenting with AUGIB in a tertiary hospital between January 1, 2019 and December 31, 2020 were analyzed and compared with data from 434 patients presenting with AUGIB at the same hospital between January 1, 2004 and December 31, 2005.

Results

Nowadays, patients were older, mean age was 69.5 (± 15.4) vs. 66.2 (± 16.0) years, they had more frequently coexisting diseases (83.5% vs. 72.8%), especially cardiovascular diseases (62.3% vs. 52.5%), and more individuals were inpatients at onset of bleeding (8.2% vs. 4.1%). In addition, more patients were under anticoagulants (18.5% vs. 6.2%), but less were under acetylsalicylic acid ± clopidogrel (36.9% vs. 33.9%). Carlson Comorbidity Index was higher nowadays (5.6 ± 6.4 vs. 3.4 ± 2.3). Moreover, a peptic ulcer was less frequently found as the cause of bleeding (38.4% vs. 56.9%), while more often nowadays endoscopy was negative (12.7% vs. 3.5%). In patients with peptic ulcer, active bleeding on endoscopy was less frequent (7.1% vs. 14.2%). Also, bleeding spots requiring hemostasis were less common on endoscopy (39.6% vs. 49.4%) and more patients were without spots of recent bleeding (49.4% vs. 38.9%). Finally, the rate of rebleeding statistically decreased (7.8% vs. 4.2%), while overall mortality remained relatively unchanged (5.0% vs. 6.2%).

Conclusions

AUGIB episodes nowadays are less severe with less peptic ulcer bleeding, but the patients are older and with more comorbidities.

Wave-packet spreading in disordered soft architected structures

We study the dynamical and chaotic behavior of a disordered one-dimensional elastic mechanical lattice, which supports translational and rotational waves. The model used in this work is motivated by the recent experimental results of Deng et al. [Nat. Commun. 9, 1 (2018)]. This lattice is characterized by strong geometrical nonlinearities and the coupling of two degrees-of-freedom (DoFs) per site. Although the linear limit of the structure consists of a linear Fermi-Pasta-Ulam-Tsingou lattice and a linear Klein-Gordon (KG) lattice whose DoFs are uncoupled, by using single site initial excitations on the rotational DoF, we evoke the nonlinear coupling between the system's translational and rotational DoFs. Our results reveal that such coupling induces rich wave-packet spreading behavior in the presence of strong disorder. In the weakly nonlinear regime, we observe energy spreading only due to the coupling of the two DoFs (per site), which is in contrast to what is known for KG lattices with a single DoF per lattice site, where the spreading occurs due to chaoticity. Additionally, for strong nonlinearities, we show that initially localized wave-packets attain near ballistic behavior in contrast to other known models. We also reveal persistent chaos during energy spreading, although its strength decreases in time as quantified by the evolution of the system's finite-time maximum Lyapunov exponent. Our results show that flexible, disordered, and strongly nonlinear lattices are a viable platform to study energy transport in combination with multiple DoFs (per site), also present an alternative way to control energy spreading in heterogeneous media.

Patients With Inflammatory Bowel Diseases Have Impaired Antibody Production After Anti-SARS-CoV-2 Vaccination: Results From a Panhellenic Registry

BACKGROUND

Four EMA-approved vaccines against SARS-CoV-2 are currently available. Data regarding antibody responses to initial vaccination regimens in patients with inflammatory bowel diseases (IBD) are limited.

METHODS

We conducted a prospective, controlled, multicenter study in tertiary Greek IBD centers. Participating patients had completed the initial vaccination regimens (1 or 2 doses, depending on the type of COVID-19 vaccine) at least 2 weeks before study enrolment. Anti-S1 IgG antibody levels were measured. Demographic and adverse events data were collected.

RESULTS

We tested 403 patients (Crohn's disease, 58.9%; male, 53.4%; median age, 45 years) and 124 healthy controls (HCs). Following full vaccination, 98% of patients seroconverted, with mRNA vaccines inducing higher seroconversion rates than viral vector vaccines (P = .021). In total, IBD patients had lower anti-S1 levels than HCs (P < .001). In the multivariate analysis, viral vector vaccines (P < .001), longer time to antibody testing (P < .001), anti-TNFα treatment (P = .013), and age (P = .016) were independently associated with lower anti-S1 titers. Vedolizumab monotherapy was associated with higher antibody levels than anti-TNFα or anti-interleukin-12/IL-23 monotherapy (P = .023 and P = .032). All anti- SARS-CoV-2 vaccines were safe.

CONCLUSIONS

Patients with IBD have impaired antibody responses to anti-SARS-CoV-2 vaccination, particularly those receiving viral vector vaccines and those on anti-TNFα treatment. Older age also hampers antibody production after vaccination. For those low-response groups, administration of accelerated or prioritized booster vaccination may be considered.

Transverse instability and dynamics of nonlocal bright solitons

We study the transverse instability and dynamics of bright soliton stripes in two-dimensional nonlocal nonlinear media. Using a multiscale perturbation method, we derive analytically the first-order correction to the soliton shape, which features an exponential growth in time-a signature of the transverse instability. The soliton's characteristic timescale associated with its exponential growth is found to depend on the square root of the nonlocality parameter. This, in turn, highlights the nonlocality-induced suppression of the transverse instability. Our analytical predictions are corroborated by direct numerical simulations, with the analytical results being in good agreement with the numerical ones.

Chilaiditi Syndrome With a Large Colonic Loop in a Patient With Autonomic Nervous System Dysfunction

Chilaiditi syndrome is an unusual condition in which radiographic evidence of a large bowel interposition between the liver and the right hemidiaphragm appears in the chest X-ray. The etiology is unknown and the clinical symptoms vary from case to case. The special characteristics of the syndrome can easily lead to a misdiagnosis and a CT scan is needed to avoid surgical interventions for a suspected pneumoperitoneum. We present a 48-year-old female patient with a medical history of autonomic nervous system dysfunction who referred to the Emergency Department (ED) due to abdominal pain. Chest radiography revealed a radiographic sign of pneumoperitoneum but a CT scan of the abdomen showed interposition of the right colon in the right hemithorax between the diaphragm and the liver without any signs of perforation. The patient was treated with bowel decompression and her symptoms resolved gradually. So far, there is no other case of Chilaiditi syndrome in a patient with autonomic nervous system dysfunction in the published literature. To conclude, Chilaiditi's sign is an unusual radiographic sign presenting as a pneumoperitoneum in the chest X-ray. In order to avoid misdiagnosis and unnecessary surgical interventions, a CT scan should be ordered.

Does radical prostatectomy result in lower urinary tract symptom improvement in high-risk and locally advanced prostate cancer? A Single-center experience

PURPOSE

Radical prostatectomy represents the most popular method of prostate cancer treatment, including cases with high-risk and locally advanced cancer. Besides, men with this disease often experience lower urinary tract symptoms (LUTS) and report high International Prostate Symptom Scores (IPSS), pathological post-void residual (PVR) urine volumes and low levels of maximum urinary flow rates (Qmax). In this study we assessed the effect of radical prostatectomy on the above parameters in patients with high-risk and locally advanced disease.

METHODS

A number of 240 individuals were enrolled in the study. Patients that required any post-operative manipulation up to the completion of 12 months after surgery were excluded. All patients were assessed pre- and post-operatively at 3, 6 and 12 months. Evaluation included IPSS, Qmax and PVR.

RESULTS

Mean age was 66.8 years. Mean PSA value was 12.7 ng/ml and mean Gleason score was 7.9. At baseline 41.3% of the patients had Qmax ⩽10 and 42.5% had IPSS >8. There was a significant increase in Qmax during the follow-up (median value was 12 at baseline and increased to 21 at 12 months). Also, IPSS and PVR decreased significantly during the follow-up. IPSS median value decreased from 9 at baseline to 5 at 12 months. Improvement was observed in all grades of symptoms.

New Compound Heterozygous Splice Site Mutations of the Skeletal Muscle Ryanodine Receptor (RYR1) Gene Manifest Fetal Akinesia: A Linkage with Congenital Myopathies

Mutations in the skeletal muscle ryanodine receptor (RYR1) gene have been linked to malignant hyperthermia susceptibility, central core disease, and minicore myopathy with external ophthalmoplegia. RYR1 is an intracellular calcium release channel and plays a crucial role in the sarcoplasmic reticulum and transverse tubule connection. Here, we report 2 fetuses from the same parents with compound heterozygous mutations in the RYR1 gene (c.10347+1G>A and c.10456-2Α>G) who presented with fetal akinesia and polyhydramnios at 27 and 19 weeks of gestation with intrauterine growth restriction in the third pregnancy. The prospective parents of the fetuses were heterozygous carriers for c.10456-2Α>G (mother) and c.10347+1G>A (father). Both mutations affect splice sites resulting in dysfunctional protein forms probably missing crucial domains of the C-terminus. Our findings reveal a new RYR1 splice site mutation (c.10456-2Α>G) that may be associated with the clinical features of myopathies, expanding the RYR1 spectrum related to these pathologies.

Prevalence of Clostridium difficile infection among hospitalized inflammatory bowel disease patients in Greece

BACKGROUND

Inflammatory bowel disease (IBD) is an independent risk factor for Clostridium difficile infection (CDI), which is associated significantly with disease severity. We aimed to determine the rates of CDI among hospitalized IBD patients in major tertiary referral hospitals in Greece.

PATIENTS AND METHODS

A retrospective analysis was carried out of stool cultures from hospitalized patients investigated for diarrhea, during 2016, tested for CDI with glutamate dehydrogenase (GDH) and toxins A and B.

RESULTS

In total, 6932 patients were tested for CDI; 894 were positive for GDH (12.89%) and 339 were also positive for C. difficile toxin (4.89%). The prevalence of CDI among all hospitalized patients was 1.6/1000 patient-days. Among these, there were 401 IBD patients, and 62 were positive for GDH (15.46%) and 30 were also positive for C. difficile toxin (7.48%). The prevalence of CDI in IBD patients was 2.5/1000 patient-days, significantly higher than in non-IBD hospitalized patients (30/401 vs. 309/6531, P=0.013). Among the 30 IBD patients (ulcerative colitis=18, Crohn's disease=12) with CDI, six were receiving biologics, three were on corticosteroids [one combined with azathioprine (AZA) and one combined with 5-ASA], nine were on AZA monotherapy and 12 were on 5-ASA monotherapy. The prevalence of CDI among patients receiving AZA monotherapy was significantly higher than in patients receiving other medications (9/68 vs. 21/333, P=0.047). Mild CDI (n=28) was treated with metronidazole and/or vancomycin, whereas severe CDI (n=2) was treated with vancomycin.

CONCLUSION

The prevalence of CDI is higher in hospitalized IBD patients than those without IBD and AZA monotherapy increases the risk of CDI.

Chaos and Anderson localization in disordered classical chains: Hertzian versus Fermi-Pasta-Ulam-Tsingou models

We numerically investigate the dynamics of strongly disordered 1D lattices under single-particle displacements, using both the Hertzian model, describing a granular chain, and the α+β Fermi-Pasta-Ulam-Tsingou model (FPUT). The most profound difference between the two systems is the discontinuous nonlinearity of the granular chain appearing whenever neighboring particles are detached. We therefore sought to unravel the role of these discontinuities in the destruction of Anderson localization and their influence on the system's chaotic dynamics. Our results show that the dynamics of both models can be characterized by: (i) localization with no chaos; (ii) localization and chaos; (iii) spreading of energy, chaos, and equipartition. The discontinuous nonlinearity of the Hertzian model is found to trigger energy spreading at lower energies. More importantly, a transition from Anderson localization to energy equipartition is found for the Hertzian chain and is associated with the "propagation" of the discontinuous nonlinearity in the chain. On the contrary, the FPUT chain exhibits an alternate behavior between localized and delocalized chaotic behavior which is strongly dependent on the initial energy excitation.

Non-Operative Management of Type 2 ERCP-Related Retroperitoneal Duodenal Perforations: A 9-Year Experience From a Single Center

Background

No consensus exists on treatment of endoscopic retrograde cholangiopancreatography (ERCP) -related, retroperitoneal duodenal perforations. The aim of this study is to determine the incidence of post-ERCP retroperitoneal periampullary (type 2) duodenal perforations and the clinical outcome of non-surgical management.

Methods

Patients who underwent ERCP in our institution during the period from January 1, 2009 to December 31, 2017 were included. Any cases of retroperitoneal periampullary duodenal (type 2) perforation were identified. Relevant data (patient characteristics, indications, radiographic findings, time to diagnosis and surgery, surgical procedures, hospital stay and outcome) were retrospectively collected and reviewed. Results were compared to those from the existing literature.

Results

There were 24 patients with retroperitoneal type 2 duodenal perforation following 4,196 ERCPs were identified (24/4196, 0.57%) over the 9-year period. ERCP indications were: choledocholithiasis, obstructive jaundice and ampullectomy (ampullary adenoma). Diagnosis (aided by CT scan) was established within the first 12 h in the majority of patients (21/24, 87.5%) and intraprocedural in 3/24, (12.5%). Twelve patients (50%) with deteriorating clinical course were managed with CT-guided percutaneous drainage. Surgical intervention was required in two (8.3%). Overall mortality was 4.2%, 1/24 (one patient died after surgery).

Conclusions

Retroperitoneal duodenal perforation is a rare and severe ERCP complication. However, conservative management is feasible in the majority of cases.

Open radical prostatectomy after transurethral resection: perioperative, functional, oncologic outcomes

INTRODUCTION

To demonstrate any differences in the perioperative, functional and oncologic outcomes after radical retropubic prostatectomy (RRP) among those patients having previously performed transurethral resection of prostate (TURP) and those not.

MATERIALS AND METHODS

A total of 35 patients were diagnosed with prostate cancer (T1a and T1b) after TURP, underwent RRP and completed a 1 year follow up (group A). They were matched with a cohort of another 35 men (group B) in terms of age, body mass index (BMI), prostatic specific antigen (PSA), Gleason score, prostate volume (before surgery), pathological stage and neurovascular bundle-sparing technique. That was a retrospective study completed between September 2011 and March 2014.

RESULTS

Not a significant difference was demonstrated among the two groups of patients concerning the functional and oncologic results. On the other hand, previous prostate surgery made the operation procedure more demanding. Besides, operative time and blood loss (though not translated in transfusion rates) were higher among patients in group A. Besides, catheter removal in group A patients was performed later than their counterparts of group B.

CONCLUSIONS

RRP after TURP is a relatively safe procedure and in the hands of experienced surgeons, a previously performed TURP, does not seem to compromise oncologic outcomes of the operation. Continence is preserved, though erectile function seems to be compromised compared with patients undergoing RRP without prior TURP. Moreover, defining the prostate and bladder neck margins can be challenging and the surgeon has to be aware of the difficulties that might confront.

Chaos and Anderson-like localization in polydisperse granular chains

We investigate the dynamics of highly polydisperse finite granular chains. From the spatiospectral properties of small vibrations, we identify which particular single-particle displacements lead to energy localization. Then, we address a fundamental question: Do granular nonlinearities and the resulting chaotic dynamics destroy this energy localization? Our numerical simulations show that for moderate nonlinearities, the overall system behaves chaotically, and spreading of energy occurs. However, long-lasting chaotic energy localization is observed for particular single-particle excitations in the presence of the nonsmooth nonlinearities. On the other hand, for sufficiently strong nonlinearities, the granular chain reaches energy equipartition. In this case, an equilibrium chaotic state is reached independent of the initial position excitation.

Acute Lower Gastrointestinal Bleeding: Characteristics and Clinical Outcome of Patients Treated With an Intensive Protocol

Background

In recent years major advances have been made in the management of patients with acute lower gastrointestinal bleeding. The aim of this study was to investigate the characteristics and clinical outcome of patients with acute lower gastrointestinal bleeding (ALGIB) treated with an intensive protocol.

Methods

We analyzed the medical records of 528 patients with ALGIB. All patients after hemodynamic stabilization underwent colonoscopy during the first 24 h of hospitalization and capsule enteroscopy when needed. Patients with massive ongoing bleeding underwent computed tomography angiography (CTA), and when active bleeding was detected embolization was immediately performed.

Results

The mean age of the patients was 70.2 ± 14.6 years and 271 (51.3%) of them were men. At least one comorbidity was present in 464 patients (87.9%), cardiovascular disease in 266 (50.4%), while 158 (30%) patients were on antiplatelet drugs and 96 (18.2%) on anticoagulants. The most common causes of bleeding were diverticulosis (19.7%) and ischemic colitis (19.3%). Thirty-six patients (6.9%) had small intestinal bleeding. In 117 patients (22.2%) active bleeding or recent bleeding stigmata were found and in 82 of them (92.1%) endoscopic hemostasis was applied. Embolization was performed in 10 (1.9%) and was successful in seven (70%) cases, while surgical hemostasis was required in only six (1.1%) cases. Forty-four (8.3%) patients had a rebleeding episode, and 13 patients died with an overall mortality of 2.5%.

Conclusions

Management of ALGIB based on an intensive protocol is safe and effective. The bleeding source can be identified in most cases with a favorable outcome.

Bright and gap solitons in membrane-type acoustic metamaterials

We study analytically and numerically envelope solitons (bright and gap solitons) in a one-dimensional, nonlinear acoustic metamaterial, composed of an air-filled waveguide periodically loaded by clamped elastic plates. Based on the transmission line approach, we derive a nonlinear dynamical lattice model which, in the continuum approximation, leads to a nonlinear, dispersive, and dissipative wave equation. Applying the multiple scales perturbation method, we derive an effective lossy nonlinear Schrödinger equation and obtain analytical expressions for bright and gap solitons. We also perform direct numerical simulations to study the dissipation-induced dynamics of the bright and gap solitons. Numerical and analytical results, relying on the analytical approximations and perturbation theory for solions, are found to be in good agreement.

Inflammatory Bowel Disease: A Potential Risk Factor for Coronary Artery Disease

Patients with inflammatory bowel disease (IBD) have a higher incidence of coronary artery disease (CAD) compared with the general population. Left main coronary artery (LMCA) thrombosis constitutes a very rare but catastrophic manifestation of acute coronary syndrome. Case reports describing young patients with IBD and LMCA thrombosis are scarce. Most importantly, patients with a positive family history of thrombotic events and those with significant genetic or acquired risk factors such as the antiphospholipid antibody syndrome, advanced age, immobilization, pregnancy, oral contraceptive use, obesity, diabetes, and cigarette smoking may have a higher risk of thrombosis among those with active IBD. We describe a 28-year-old man who was admitted for coronary angiography (CA) due to ST-segment elevation myocardial infarction. He had a recent exacerbation of ulcerative colitis. The patient was a smoker without a family history of CAD. Proximal total occlusion of the left anterior descending (LAD) artery and left circumflex (LCX) artery with massive thrombus was shown on CA, whereas a normal dominant right coronary artery delivered collaterals to the LAD artery.

Recurrence of choledocholithiasis following endoscopic bile duct clearance: Long term results and factors associated with recurrent bile duct stones

AIM

To evaluate the rate of recurrence of symptomatic choledocholithiasis and identify factors associated with the recurrence of bile duct stones in patients who underwent endoscopic retrograde cholangiopancreatography (ERCP) and endoscopic sphincterotomy (EST) for bile duct stone disease.

METHODS

All patients who underwent ERCP and EST for bile duct stone disease and had their bile duct cleared from 1/1/2005 until 31/12/2008 was enrolled. All symptomatic recurrences during the study period (until 31/12/2015) were recorded. Clinical and laboratory data potentially associated with common bile duct (CBD) stone recurrence were retrospectively retrieved from patients’ files.

RESULTS

A total of 495 patients were included. Sixty seven (67) out of 495 patients (13.5%) presented with recurrent symptomatic choledocholithiasis after 35.28 ± 16.9 mo while twenty two (22) of these patients (32.8%) experienced a second recurrence after 35.19 ± 23.2 mo. Factors associated with recurrence were size (diameter) of the largest CBD stone found at first presentation (10.2 ± 6.9 mm vs 7.2 ± 4.1 mm, P = 0.024), diameter of the CBD at the first examination (15.5 ± 6.3 mm vs 12.0 ± 4.6 mm, P = 0.005), use of mechanical lithotripsy (ML) (P = 0.04) and presence of difficult lithiasis (P = 0.04). Periampullary diverticula showed a trend towards significance (P = 0.066). On the contrary, number of stones, angulation of the CBD, number of ERCP sessions required to clear the CBD at first presentation, more than one ERCP session needed to clear the bile duct initially and a gallbladder in situ did not influence recurrence.

CONCLUSION

Bile duct stone recurrence is a possible late complication following endoscopic stone extraction and CBD clearance. It appears to be associated with anatomical parameters (CBD diameter) and stone characteristics (stone size, use of ML, difficult lithiasis) at first presentation.

Predictors of tissue healing in ulcerative colitis patients treated with anti-TNF

AIM

To identify factors predicting mucosal healing in ulcerative colitis patients treated with anti-TNFα agents with or without azathioprine.

METHODS

In a prospective, multicenter, one-year study biologic naïve patients aged 25-65 years, with corticosteroid-dependent or refractory colitis received combination treatment with anti-TNFα and azathioprine for 6 months followed by anti-TNFα monotherapy. Patients who denied combination therapy or were outside this age range received anti-TNFα monotherapy (controls). Before and at weeks 12 and 54 of treatment the total Mayo score was calculated. Mucosal healing was defined as endoscopic subscore of 0. Mucosal expression of T helper (Th) cell-lineage specific transcription factors (Tbet, Gata3, Rorc, FoxP3) before treatment was also associated with mucosal healing.

RESULTS

Of 67 patients, 58 (86.6%) received combination and 9 (13.4%) anti-TNFα monotherapy. Overall 29 (43.3%) patients achieved mucosal healing; rates were higher in patients receiving combination therapy vs. monotherapy (p=0.03) and in azathioprine naïve vs. exposed patients in the combination group (p=0.01). Mucosal healing was associated with lower pre-treatment mucosal expression of transcription factor Th1-Tbet (p<0.05) and higher expression of Th17-Rorc (p<0.05).

CONCLUSIONS

Mucosal healing was associated with combination therapy, especially in biologic and azathioprine-naïve patients and pre-treatment mucosal expression of specific Th specific transcripting factors (Tbet and Rorc).

Zero-frequency and slow elastic modes in phononic monolayer granular membranes

We theoretically study the dispersion properties of elastic waves in hexagonal and honeycomb monolayer granular membranes with either out-of-plane or in-plane particle motion. The particles interact predominantly via normal and transverse contact rigidities. When rotational degrees of freedom are taken into account, the bending and torsional rigidities of the intergrain contacts can control some of the phononic modes. The existence of zero-frequency modes, zero-group-velocity modes and their transformation into slow propagating phononic modes due to weak bending and torsional intergrain interactions are investigated. We also study the formation and manipulation of Dirac cones and multiple degenerated modes. This could motivate variety of potential applications in elastic waves control by manipulating the contact rigidities in granular phononic crystals.

Coherent perfect absorption induced by the nonlinearity of a Helmholtz resonator

In this work, coherent perfect absorption of sound waves induced by the nonlinear response of a Helmholtz Resonator side loaded to a waveguide, is reported. It is shown that this two-port system can perfectly absorb two high amplitude symmetric incident waves under a certain condition. For the one-sided incidence configuration, this condition leads to an absorption equal to 0.5. Experiments verify these results and are in agreement with an analytical nonlinear impedance model for the resonator. The nonlinear control of perfect absorption opens new possibilities in the design of high amplitude sound attenuators for aero-engine applications.

Use of complex frequency plane to design broadband and sub-wavelength absorbers

The reflection of sound of frequency below 1 kHz, by a rigid-backed structure that contains sub-wavelength resonators is studied in this work. In particular, only single mode reflected waves are considered, an approximation which is accurate in this low frequency regime. A method of analysis of absorption that uses the structure of the reflection coefficient in the complex frequency plane is proposed. In the absence of losses, the reflection coefficient supports pairs of poles and zeros that are complex conjugate and which have imaginary parts linked to the energy leakage by radiation. When losses are introduced and balanced to the leakage, the critical coupling condition is satisfied and total absorption is obtained. Examples of a slot resonator and of multiple Helmholtz resonators are analyzed to obtain both narrow and broadband total absorption.

Decreased Serotonin Levels and Serotonin-Mediated Osteoblastic Inhibitory Signaling in Patients With Ankylosing Spondylitis

Evidence suggests that serotonin is an inhibitor of bone formation. We aimed to assess: 1) serum serotonin levels in patients with ankylosing spondylitis (AS), a prototype bone-forming disease, compared with patients with rheumatoid arthritis (RA) and healthy subjects; 2) the effect(s) of TNFα blockers on serum serotonin levels in patients with AS and RA; and 3) the effect(s) of serum of AS patients on serotonin signaling. Serum serotonin levels were measured in 47 patients with AS, 28 patients with RA, and 40 healthy subjects by radioimmunoassay; t test was used to assess differences between groups. The effect of serum on serotonin signaling was assessed using the human osteoblastic cell line Saos2, evaluating levels of phospho-CREB by Western immunoblots. Serotonin serum levels were significantly lower in patients with AS compared with healthy subjects (mean ± SEM ng/mL 122.9 ± 11.6 versus 177.4 ± 24.58, p = 0.038) and patients with RA (mean ± SEM ng/mL 244.8 ± 37.5, p = 0.0004). Patients with AS receiving TNFα blockers had significantly lower serotonin levels compared with patients with AS not on such treatment (mean ± SEM ng/mL 95.8 ± 14.9 versus 149.2 ± 16.0, p = 0.019). Serotonin serum levels were inversely correlated with pCREB induction in osteoblast-like Saos-2 cells. Serotonin levels are low in patients with AS and decrease even further during anti-TNFα treatment. Differences in serotonin levels are shown to have a functional impact on osteoblast-like Saos-2 cells. Therefore, serotonin may be involved in new bone formation in AS.

Energy transport in one-dimensional disordered granular solids

We investigate the energy transport in one-dimensional disordered granular solids by extensive numerical simulations. In particular, we consider the case of a polydisperse granular chain composed of spherical beads of the same material and with radii taken from a random distribution. We start by examining the linear case, in which it is known that the energy transport strongly depends on the type of initial conditions. Thus, we consider two sets of initial conditions: an initial displacement and an initial momentum excitation of a single bead. After establishing the regime of sufficiently strong disorder, we focus our study on the role of nonlinearity for both sets of initial conditions. By increasing the initial excitation amplitudes we are able to identify three distinct dynamical regimes with different energy transport properties: a near linear, a weakly nonlinear, and a highly nonlinear regime. Although energy spreading is found to be increasing for higher nonlinearities, in the weakly nonlinear regime no clear asymptotic behavior of the spreading is found. In this regime, we additionally find that energy, initially trapped in a localized region, can be eventually detrapped and this has a direct influence on the fluctuations of the energy spreading. We also demonstrate that in the highly nonlinear regime, the differences in energy transport between the two sets of initial conditions vanish. Actually, in this regime the energy is almost ballistically transported through shocklike excitations.

Nonlinear Hysteretic Torsional Waves

We theoretically study and experimentally report the propagation of nonlinear hysteretic torsional pulses in a vertical granular chain made of cm-scale, self-hanged magnetic beads. As predicted by contact mechanics, the torsional coupling between two beads is found to be nonlinear hysteretic. This results in a nonlinear pulse distortion essentially different from the distortion predicted by classical nonlinearities and in a complex dynamic response depending on the history of the wave particle angular velocity. Both are consistent with the predictions of purely hysteretic nonlinear elasticity and the Preisach-Mayergoyz hysteresis model, providing the opportunity to study the phenomenon of nonlinear dynamic hysteresis in the absence of other types of material nonlinearities. The proposed configuration reveals a plethora of interesting phenomena including giant amplitude-dependent attenuation, short-term memory, as well as dispersive properties. Thus, it could find interesting applications in nonlinear wave control devices such as strong amplitude-dependent filters.

Highly nonlinear wave propagation in elastic woodpile periodic structures

In the present work, we experimentally implement, numerically compute with, and theoretically analyze a configuration in the form of a single column woodpile periodic structure. Our main finding is that a Hertzian, locally resonant, woodpile lattice offers a test bed for the formation of genuinely traveling waves composed of a strongly localized solitary wave on top of a small amplitude oscillatory tail. This type of wave, called a nanopteron, is not only motivated theoretically and numerically, but is also visualized experimentally by means of a laser Doppler vibrometer. This system can also be useful for manipulating stress waves at will, for example, to achieve strong attenuation and modulation of high-amplitude impacts without relying on damping in the system.

Wave propagation in granular chains with local resonances

We study wave propagation in a chain of spherical particles containing a local resonator. The resonant particles are made of an aluminum outer spherical shell and a steel inner mass connected by a polymeric plastic structure acting as a spring. We characterize the dynamic response of individual particles and the transmitted linear spectra of a chain of particles in contact. A wide band gap is observed both in theoretical and experimental results. We show the ability to tune the acoustic transmission by varying the contact interaction between particles. Higher driving amplitude leads to the generation of nonlinearities both in the response of a single particle and that of the whole chain. For a single resonant particle, we observe experimentally a resonant frequency downshift, which follows a complex nonlinear behavior. In the chain of particles, nonlinearity leads to the generation of nonlinear harmonics and the presence of localized modes inside the band gap.

Acoustic solitons in waveguides with Helmholtz resonators: transmission line approach

We report experimental results and study theoretically soliton formation and propagation in an air-filled acoustic waveguide side loaded with Helmholtz resonators. We propose a theoretical modeling of the system, which relies on a transmission-line approach, leading to a nonlinear dynamical lattice model. The latter allows for an analytical description of the various soliton solutions for the pressure, which are found by means of dynamical systems and multiscale expansion techniques. These solutions include Boussinesq-like and Korteweg-de Vries pulse-shaped solitons that are observed in the experiment, as well as nonlinear Schrödinger envelope solitons, that are predicted theoretically. The analytical predictions are in excellent agreement with direct numerical simulations and in qualitative agreement with the experimental observations.

Nonlinear resonances and energy transfer in finite granular chains

In the present work we test experimentally and compute numerically the stability and dynamics of harmonically driven monoatomic granular chains composed of an increasing number of particles N(N=1-50). In particular, we investigate the inherent effects of dissipation and finite size on the evolution of bifurcation instabilities in the statically compressed case. The findings of the study suggest that the nonlinear bifurcation phenomena, which arise due to finite size, can be useful for efficient energy transfer away from the drive frequency in transmitted waves.

Dark breathers in granular crystals

We present a study of the existence, stability, and bifurcation structure of families of dark breathers in a one-dimensional uniform chain of spherical beads under static load. A defocusing nonlinear Schrödinger equation (NLS) is derived for frequencies that are close to the edge of the phonon band and is used to construct targeted initial conditions for numerical computations. Salient features of the system include the existence of large amplitude solutions that emerge from the small amplitude solutions described by the NLS equation, and the presence of a nonlinear instability that, to the best of the authors' knowledge, has not been observed in classical Fermi-Pasta-Ulam lattices. Finally, it is also demonstrated that these dark breathers can be detected in a physically realistic experimental settings by merely actuating the ends of an initially at rest chain of beads and inducing destructive interference between their signals.

Association between use of air-conditioning or fan and survival of elderly febrile patients: a prospective study

Elderly individuals are more susceptible to excess summer heat. We sought to examine whether the use of cooling systems (air-conditioning or fan) affected the clinical outcomes of elderly febrile patients. We prospectively followed elderly (≥ 75 years old) febrile patients requesting the medical services of the SOS Doctors (a network of physicians performing house-call visits) from July 10 to August 20, 2011. Patients who used cooling systems ("users") were compared with those who did not ("non-users") regarding mortality, clinical outcome of primary illness (improvement or deterioration), and emergency hospitalization. Prospectively collected data were available for 339 individual elderly febrile patients. "Users" had lower mortality (10 % vs. 19 %, p < 0.05) than "non-users"; no difference was noted on clinical improvement (85 % vs. 76 %, p = 0.11) and emergency hospitalization rates (21 % vs. 30 %, p = 0.16). No difference was noted between users of air-conditioning and fan regarding mortality or clinical improvement, but fan use was associated with more hospitalizations (37 % vs. 19 %, p < 0.05). On multivariate analysis (assessing daily ambient temperature, use of cooling systems, patient age, and living conditions), the sole variable significantly associated with mortality was the non-use of cooling systems [odds ratio (OR): 2.18, 95 % confidence interval (CI): 1.06-4.50]. The use of air-conditioning or fan during hot summer periods appeared to be beneficial for elderly febrile patients living in a large city. Large prospective studies are warranted in order to provide further insight into potential individual and public health initiatives aiming to alleviate the impact of excess summer heat on the health of elderly patients.

Health-related quality of life in patients with inflammatory bowel disease: a single-center experience

BACKGROUND

Inflammatory bowel disease (IBD) has a negative impact on health-related quality of life (HRQoL). The aim of the study was to assess HRQoL of IBD patients in South-Western Greece.

METHODS

89 IBD patients [38 (42.7%) Crohn's disease (CD), 51 (57.3%) ulcerative colitis (UC)] were included. HRQoL was assessed using IBD questionnaire (IBDQ), which tests four health domains: bowel symptoms (BS), systemic symptoms (SS), emotional function (EF) and social function (SF). Total score (TS) ranges from 32 to 224. Disease activity was measured using Crohn's Disease Activity Index (CDAI) (CD), and Truelove and Witts classification (UC). The impact of epidemiological and disease-specific characteristics on IBDQ was studied.

RESULTS

No statistically significant difference was found in all IBDQ scores between UC and CD patients. No correlation was found regarding age, sex, smoking, anemia, disease duration and use of corticosteroids, 5-aminosalicylates or immunosuppressives with HRQoL. The factors found to have a major negative impact on all IBDQ scores was disease severity both in CD and UC, and education on bowel symptoms in CD. On multivariate analysis, only high disease activity had significant effects on total and dimensional scores of IBDQ in UC (TS, P=0.005; BS, P<0.001; SS, P=0.004; EF, P=0.05; SF, P=0.001), whereas in CD, only CDAI (TS, P=0.001; BS, P=0.004; SS, P=0.001; EF, P=0.003; SF, P=0.003) and education (TS, P=0.047; BS, P=0.004; SS, P=0.03) had significant effects.

CONCLUSIONS

IBD patients in remission experience better HRQoL than patients with active disease. Induction of remission should become the mainstay of care regarding improvement in HRQoL.

Defect modes in one-dimensional granular crystals

We study the vibrational spectra of one-dimensional statically compressed granular crystals (arrays of elastic particles in contact) containing light-mass defects. We focus on the prototypical settings of one or two spherical defects (particles of smaller radii) interspersed in a chain of larger uniform spherical particles. We present a systematic measurement, using continuous noise, of the near-linear frequency spectrum within the spatial vicinity of the defect(s). Using this technique, we identify the frequencies of the localized defect modes as a function of the defect size and the position of the defects relative to each other. We also compare the experimentally determined frequencies with those obtained by numerical eigenanalysis and by analytical expressions based on few-site considerations. These approximate analytical expressions, based on normal-mode analysis, are found to be in excellent agreement with numerics for a wide range of mass ratios. We also observe that the experimentally measured frequencies of the localized defect modes are uniformly upshifted, compared to the numerically and theoretically predicted values.

Comparison of morbidity of elderly patients in August and November in Attica, Greece: a prospective study

BACKGROUND

In our clinical practice, we have experienced a consistent increase in the morbidity of elderly in Greece during August.

METHODS

We prospectively analysed and compared the morbidity of elderly patients (≥ 75 years old) between August and November of the same year (2010), using data from the SOS Doctors (a network of physicians performing house call visits).

RESULTS

We analysed data on 739 and 738 elderly patient house-calls in August and November, respectively. Overall, the most common diagnoses were cardiovascular (17.6%), musculoskeletal (10.7%), gastrointestinal (9.5%), respiratory (8.5%), renal/genitourinary (8.1%), and neurologic/psychiatric (7.9%). In August, patients were older (p < 0.01), carried a heavier burden of disease (as inferred by specific types of comorbidity and associated medical conditions), were more frequently recommended emergency hospitalization (p < 0.01) and had a worse outcome of primary illness (p < 0.05). Mortality of elderly visited in August was significantly higher compared to November (5% vs. 2%, p < 0.01). The sole independent predictor of mortality was patient's bedridden status [adjusted odds ratio (OR) = 5.59, 95% confidence intervals (CI) 2.83-11.06, p < 0.001]. The identified independent predictors of recommendation for emergency hospitalization were patient's lethargic status [OR = 2.88 (1.80, 4.59), p < 0.001], fever [OR = 2.55 (1.84, 3.54), p < 0.001], heat stroke [OR = 2.08 (1.19, 3.64), p = 0.01], Alzheimer's disease [OR = 1.77 (1.15, 2.72), p = 0.01] and bedridden status [OR = 1.45 (1.07, 1.97), p < 0.05].

CONCLUSION

Morbidity and mortality of elderly patients was significantly higher in August compared with November, substantiating the informal term 'Augustitis' for the Greek elderly. Large, prospective population-based studies are warranted to further enlighten this field.

Comparison of characteristics of outpatients with 2009 H1N1 pandemic and seasonal influenza

BACKGROUND

The latest influenza pandemic intensified the interest in this infection.

OBJECTIVE

We aimed to compare the characteristics of outpatients with seasonal and pandemic influenza.

METHODS

We retrospectively reviewed data regarding outpatients who sought medical advice from a network of physicians performing house-call visits at the area of Attica, Greece, and who underwent a direct influenza test during the period of seasonal influenza (1/1/2009-1/5/2009) and 2009 H1N1 pandemic influenza period (17/5/2009-15/4/2010).

RESULTS

A total of 195 and 1317 patients had a direct influenza test during the seasonal and pandemic influenza period, respectively; 50.7% and 32% of these patients had a positive test result for influenza, respectively. Viral culture or polymerase chain reaction (PCR) were not implemented. Patients found positive for influenza during the pandemic period, compared with those evaluated during the seasonal period, were younger (mean age ± SD: 33 ± 17.2 vs. 38.2 ± 19.2, p = 0.008), more likely to have no comorbidity (62.9% vs. 45.5%, p = 0.002), had milder clinical manifestations, and were treated with more antibiotics (38.3% vs. 9.9%, p < 0.001). However, patients found positive during the seasonal period were treated with more antivirals (oseltamivir: 69.1% vs. 85.7%, p = 0.006). No difference was observed regarding the need for immediate hospitalisation. These findings were consistent in the complementary analysis involving patients tested for influenza during the compared periods.

CONCLUSION

Despite the methodological limitations, our findings suggest that patients with pandemic influenza were younger, had milder clinical manifestations and were less likely to have any kind of comorbidity compared with patients with seasonal influenza.

Bifurcation-based acoustic switching and rectification

Switches and rectification devices are fundamental components used for controlling the flow of energy in numerous applications. Thermal and acoustic rectifiers have been proposed for use in biomedical ultrasound applications, thermal computers, energy- saving and -harvesting materials, and direction-dependent insulating materials. In all these systems the transition between transmission states is smooth with increasing signal amplitudes. This limits their effectiveness as switching and logic devices, and reduces their sensitivity to external conditions as sensors. Here we overcome these limitations by demonstrating a new mechanism for tunable rectification that uses bifurcations and chaos. This mechanism has a sharp transition between states, which can lead to phononic switching and sensing. We present an experimental demonstration of this mechanism, applied in a mechanical energy rectifier operating at variable sonic frequencies. The rectifier is a granular crystal, composed of a statically compressed one-dimensional array of particles in contact, containing a light mass defect near a boundary. As a result of the defect, vibrations at selected frequencies cause bifurcations and a subsequent jump to quasiperiodic and chaotic states with broadband frequency content. We use this combination of frequency filtering and asymmetrically excited bifurcations to obtain rectification ratios greater than 10(4). We envisage this mechanism to enable the design of advanced photonic, thermal and acoustic materials and devices.

Discrete breathers at the interface between a diatomic and a monoatomic granular chain

In the present work, we develop a systematic examination of the existence, stability, and dynamical properties of a discrete breather at the interface between a diatomic and a monoatomic granular chain. We remarkably find that such an "interface breather" is more robust than its bulk diatomic counterpart throughout the gap of the linear spectrum. The latter linear spectral gap needs to exist for the breather state to arise and the relevant spectral conditions are discussed. We illustrate the minimal excitation conditions under which such an interface breather can be "nucleated" and analyze its apparently weak interaction with regular highly nonlinear solitary waveforms.

Intrinsic energy localization through discrete gap breathers in one-dimensional diatomic granular crystals

We present a systematic study of the existence and stability of discrete breathers that are spatially localized in the bulk of a one-dimensional chain of compressed elastic beads that interact via Hertzian contact. The chain is diatomic, consisting of a periodic arrangement of heavy and light spherical particles. We examine two families of discrete gap breathers: (1) an unstable discrete gap breather that is centered on a heavy particle and characterized by a symmetric spatial energy profile and (2) a potentially stable discrete gap breather that is centered on a light particle and is characterized by an asymmetric spatial energy profile. We investigate their existence, structure, and stability throughout the band gap of the linear spectrum and classify them into four regimes: a regime near the lower optical band edge of the linear spectrum, a moderately discrete regime, a strongly discrete regime that lies deep within the band gap of the linearized version of the system, and a regime near the upper acoustic band edge. We contrast discrete breathers in anharmonic Fermi-Pasta-Ulam (FPU)-type diatomic chains with those in diatomic granular crystals, which have a tensionless interaction potential between adjacent particles, and note that the asymmetric nature of the tensionless interaction potential can lead to hybrid bulk-surface localized solutions.

Discrete breathers in one-dimensional diatomic granular crystals

We report the experimental observation of modulational instability and discrete breathers in a one-dimensional diatomic granular crystal composed of compressed elastic beads that interact via Hertzian contact. We first characterize their effective linear spectrum both theoretically and experimentally. We then illustrate theoretically and numerically the modulational instability of the lower edge of the optical band. This leads to the dynamical formation of long-lived breather structures, whose families of solutions we compute throughout the linear spectral gap. Finally, we experimentally observe the manifestation of the modulational instability and the resulting generation of localized breathing modes with quantitative characteristics that agree with our numerical results.

Localized breathing modes in granular crystals with defects

We study localized modes in uniform one-dimensional chains of tightly packed and uniaxially compressed elastic beads in the presence of one or two light-mass impurities. For chains composed of beads of the same type, the intrinsic nonlinearity, which is caused by the Hertzian interaction of the beads, appears not to support localized, breathing modes. Consequently, the inclusion of light-mass impurities is crucial for their appearance. By analyzing the problem's linear limit, we identify the system's eigenfrequencies and the linear defect modes. Using continuation techniques, we find the solutions that bifurcate from their linear counterparts and study their linear stability in detail. We observe that the nonlinearity leads to a frequency dependence in the amplitude of the oscillations, a static mutual displacement of the parts of the chain separated by a defect, and for chains with two defects that are not in contact, it induces symmetry-breaking bifurcations.

Two-dimensional paradigm for symmetry breaking: the nonlinear Schrödinger equation with a four-well potential

We study the existence and stability of localized modes in the two-dimensional (2D) nonlinear Schrödinger/Gross-Pitaevskii (NLS/GP) equation with a symmetric four-well potential. Using the corresponding four-mode approximation, we trace the parametric evolution of the trapped stationary modes, starting from the linear limit, and thus derive a complete bifurcation diagram for families of the stationary modes. This provides the picture of spontaneous symmetry breaking in the fundamental 2D setting. In a broad parameter region, the predictions based on the four-mode decomposition are found to be in good agreement with full numerical solutions of the NLS/GP equation. Stability properties of the stationary states coincide with those suggested by the corresponding discrete model in the large-amplitude limit. The dynamics of unstable modes is explored by means of direct simulations. Finally, in addition to the full analysis for the case of the self-attractive nonlinearity, the bifurcation diagram for the case of self-repulsion is briefly considered too.