Geometrical frustration and cluster spin glass with random graphs

We develop a based on a sparse random graph to account for the interplay between geometric frustration and disorder in cluster magnetism. Our theory allows introduction of the cluster network connectivity as a controllable parameter. Two types of inner cluster geometry are considered: triangular and tetrahedral. The theory was developed for general, nonuniform intracluster interactions, but in the present paper the results presented correspond to uniform, antiferromagnetic (AF) intraclusters interaction J_{0}/J. The clusters are represented by nodes on a finite connectivity random graph, and the intercluster interactions are randomly Gaussian distributed. The graph realizations are treated in replica theory using the formalism of order parameter functions, which allows one to calculate the distribution of local fields and, as a consequence, the relevant observable. In the case of triangular cluster geometry, there is the onset of a classical spin liquid state at a temperature T^{*}/J and then, a cluster spin glass (CSG) phase at a temperature T_{/}J. The CSG ground state is robust even for very weak disorder or large negative J_{0}/J. These results does not depend on the network connectivity. Nevertheless, variations in the connectivity strongly affect the level of frustration f_{p}=-Θ_{CW}/T_{f} for large J_{0}/J. In contrast, for the nonfrustrated tetrahedral cluster geometry, the CSG ground state is suppressed for weak disorder or large negative J_{0}/J. The CSG boundary phase presents a reentrance which is dependent on the network connectivity.

Ising spin glass in a random network with a Gaussian random field

We investigate thermodynamic phase transitions of the joint presence of spin glass (SG) and random field (RF) using a random graph model that allows us to deal with the quenched disorder. Therefore, the connectivity becomes a controllable parameter in our theory, allowing us to answer what the differences are between this description and the mean-field theory i.e., the fully connected theory. We have considered the random network random field Ising model where the spin exchange interaction as well as the RF are random variables following a Gaussian distribution. The results were found within the replica symmetric (RS) approximation, whose stability is obtained using the two-replica method. This also puts our work in the context of a broader discussion, which is the RS stability as a function of the connectivity. In particular, our results show that for small connectivity there is a region at zero temperature where the RS solution remains stable above a given value of the magnetic field no matter the strength of RF. Consequently, our results show important differences with the crossover between the RF and SG regimes predicted by the fully connected theory.

Stoma reversal after intended restorative rectal cancer resection in Denmark: nationwide population-based study

BACKGROUND

Data on stoma reversal following restorative rectal resection (RRR) with a diverting stoma are conflicting. This study investigated a Danish population-based cohort of patients undergoing RRR to evaluate factors predictive of stoma reversal during 3 years of follow-up.

METHODS

Patients from national registries with rectal cancer undergoing RRR or Hartmann's procedure with curative intent between May 2001 and April 2012 were included. Patients with a diverting stoma were followed from the time of primary rectal cancer resection to date of stoma reversal, death, emigration, or end of 3-year follow-up. The cumulative incidence proportion (CIP) of stoma reversal at 1 and 3 years was calculated, treating death as a competing risk. Factors predictive of stoma reversal were explored using Cox regression analysis.

RESULTS

Of 6859 patients included, 35·7, 41·9 and 22·4 per cent respectively had a RRR with a diverting stoma, RRR without a stoma, and Hartmann's procedure with an end-colostomy. In patients with a diverting stoma, the CIP of stoma reversal was 70·3 (95 per cent c.i. 68·4 to 72·1) per cent after 1 year, and 74·3 (72·5 to 76·0) per cent after 3 years. Neoadjuvant treatment (hazard ratio (HR) 0·75, 95 per cent c.i. 0·66 to 0·85), blood loss greater than 300 ml (HR 0·86, 0·76 to 0·97), anastomotic leak (HR 0·41, 0·33 to 0·50), T3 category (HR 0·63, 0·47 to 0·83), T4 category (HR 0·62, 0·42 to 0·90) and UICC stage IV (HR 0·57, 0·41 to 0·80) were possible predictors of delayed stoma reversal.

CONCLUSION

In one-quarter of the patients the diverting stoma had not been reversed 3 years after the intended RRR procedure.

Pouch failures following ileal pouch-anal anastomosis for ulcerative colitis

AIM

Ileal pouch-anal anastomosis is a procedure offered to patients with ulcerative colitis who opt for restoration of bowel continuity. The aim of this study was to determine the risk of pouch failure and ascertain the risk factors associated with failure.

METHOD

The study included 1991 patients with ulcerative colitis who underwent ileal pouch-anal anastomosis in Denmark in the period 1980-2013. Pouch failure was defined as excision of the pouch or presence of an unreversed stoma within 1 year after its creation. We used Cox proportional hazards regression to explore the association between pouch failure and age, gender, synchronous colectomy, primary faecal diversion, annual hospital volume (very low, 1-5 cases per year; low, 6-10; intermediate 11-20; high > 20), calendar year, laparoscopy and primary sclerosing cholangitis.

RESULTS

Over a median 11.4 years, 295 failures occurred, corresponding to 5-, 10- and 20-year cumulative risks of 9.1%, 12.1% and 18.2%, respectively. The risk of failure was higher for women [adjusted hazard ratio (aHR) 1.39, 95% CI 1.10-1.75]. Primary non-diversion (aHR 1.63, 95% CI 1.11-2.41) and a low hospital volume (aHR, very low volume vs high volume 2.30, 95% CI 1.26-4.20) were also associated with a higher risk of failure. The risk of failure was not associated with calendar year, primary sclerosing cholangitis, synchronous colectomy or laparoscopy.

CONCLUSION

In a cohort of patients from Denmark (where pouch surgery is centralized) with ulcerative colitis and ileal pouch-anal anastomosis, women had a higher risk of pouch failure. Of modifiable factors, low hospital volume and non-diversion were associated with a higher risk of pouch failure.

Nationwide population-based cohort study to assess risk of surgery for adhesive small bowel obstruction following open or laparoscopic rectal cancer resection

Background

Laparoscopic surgery has been reported to reduce the formation of adhesions following colorectal surgery. The aim of this nationwide cohort study was to investigate the risk of surgery for adhesive small bowel obstruction (SBO) following open and laparoscopic rectal cancer resection.

Methods

Patients undergoing rectal cancer resection between 2005 and 2013 were identified in the Danish Colorectal Cancer Group database. The primary outcome of surgery for adhesive SBO was identified in the Danish National Patient Registry. The risk of surgery for adhesive SBO was estimated as the cumulative incidence proportion, treating death as a competing risk. Cox proportional hazards regression analysis with multivariable adjustment was used to compute hazard ratios (HRs). The secondary outcome was 30‐day mortality after surgery for adhesive SBO.

Results

Of 7657 patients, 340 (4·4 per cent) underwent surgery for adhesive SBO. The 5‐year risk of surgery for adhesive SBO was 4·5 per cent among 4472 patients undergoing open resection and 3·0 per cent among 3185 patients having a laparoscopic resection. Laparoscopic rectal resection was associated with a lower risk of subsequent operation for adhesive SBO (adjusted HR 0·65, 95 per cent c.i. 0·50 to 0·86; P = 0·002). The adjusted HR of mortality after adhesive SBO was 0·84 (0·37 to 1·91; P = 0·671) comparing patients with previous laparoscopic and open resection.

Conclusion

Laparoscopic rectal cancer resection was associated with a decreased risk of surgery for adhesive SBO. There was a substantial difference in 30‐day mortality after surgery for adhesive SBO based on the surgical approach used at the time of rectal resection.

Multicritical points and topology-induced inverse transition in the random-field Blume-Capel model in a random network

The interplay between quenched disorder provided by a random field (RF) and network connectivity in the Blume-Capel (BC) model is the subject of this paper. The replica method is used to average over the network randomness. It offers an alternative analytic route to both numerical simulations and standard mean field approaches. The results reveal a rich thermodynamic scenario with multicritical points that are strongly dependent on network connectivity. In addition, we also demonstrate that the RF has a deep effect on the inverse melting transition. This highly nontrivial type of phase transition has been proposed to exist in the BC model as a function of network topology. Our results confirm that the topological mechanism can lead to an inverse melting transition. Nevertheless, our results also show that as the RF becomes stronger, the paramagnetic phase is affected in such way that the topological mechanism for inverse melting is disabled.

Corticosteroid use and mortality risk in patients with perforated colonic diverticular disease: a population-based cohort study

Background

Corticosteroids are a potential risk factor for mortality in patients with perforated diverticular disease, due to blinding of disease severity, hampered wound healing or adrenal insufficiency. We examined mortality in corticosteroid users and non-users among patients with perforated diverticular disease.

Methods

A cohort study based on medical databases including all patients ≥18 years in Denmark (source population 5 289 261 inhabitants) admitted to a hospital with incident perforated diverticular disease between 2005 and 2013. 7-day, 1-month, 3-month and 1-year mortality risks in corticosteroid users and non-users were calculated using the Kaplan–Meier method, and compared with Cox proportional hazard regression adjusted for age, sex and comorbidities.

Results

The study included 4640 patients with perforated diverticular disease. Of these, 3743 (80.7%) had not used corticosteroids in the year before admission and 725 (15.6%) had been exposed to systemic corticosteroid treatment. The remaining 172 patients had been exposed to either inhaled or intestinal acting corticosteroid therapy. Mortality risk in non-users was 4.4% after 7 days and 15.6% after 1 year. This risk was doubled for corticosteroid users who filled their last prescription during the 90 days before admission, with mortality risks ranging from 14.2% after 7 days to 47.6% after 1 year. 1-year mortality risk was even higher for corticosteroid users with a first filled prescription ≤90 days before admission: 52.5%.

Conclusions

Corticosteroid use was associated with clearly increased mortality risk after perforated diverticular disease. Thus, use of corticosteroids should be regarded as an important clinical prognostic factor for mortality in patients with this condition.

Mortality and cardiovascular diseases risk in patients with Barrett's oesophagus: a population-based nationwide cohort study

BACKGROUND

Patients with Barrett's oesophagus may be at increased risk of mortality overall, and cardiovascular disease has been suggested as the main underlying cause of death.

AIM

To examine cause-specific mortality and risk of cardiovascular events among patients with Barrett's oesophagus.

METHODS

Utilising existing Danish data sources (1997-2011), we identified all patients with histologically verified Barrett's oesophagus (n = 13 435) and 123 526 members of the general population matched by age, sex and individual comorbidities. We calculated cause-specific mortality rates and incidence rates of cardiovascular diseases. We then compared rates between patients with Barrett's oesophagus and the general population comparison cohort, using stratified Cox proportional hazard regression.

RESULTS

Patients with Barrett's oesophagus had a 71% increased risk of overall mortality. The cause-specific mortality rate per 1000 person-years for patients with Barrett's oesophagus was 8.5 for cardiovascular diseases, 14.7 for non-oesophageal cancers, and 5.4 for oesophageal cancer. Compared to the general population cohort, corresponding hazard ratios were 1.26 (95% confidence interval (CI): 1.15-1.38), 1.77 (95% CI: 1.65-1.90), and 19.4 (95% CI: 16.1-23.4), respectively. The incidence rates of cardiovascular diseases per 1000 person-years for Barrett's oesophagus patients and for persons from the general population cohort, respectively, varied from 0.4 and 0.2 for subarachnoid bleeding (hazard ratio 1.10, 95% CI: 0.87-1.39) to 8.1 and 5.9 for congestive heart failure (hazard ratio 1.33, 95% CI: 1.21-1.46).

CONCLUSION

Prophylactic measures targeted at cardiovascular diseases and non-oesophageal cancers potentially could be more important than measures against oesophageal cancer, for improving prognosis among patients with Barrett's oesophagus.

Inflammatory bowel disease and venous thromboembolism during pregnancy and the postpartum period

Essentials Risk of pregnancy-related venous thromboembolism may be increased in inflammatory bowel disease. We performed a study on inflammatory bowel disease and pregnancy-related venous thromboembolism. Inflammatory bowel disease is a risk factor for pregnancy-related venous thromboembolism. Proper disease control before conception is pivotal to avoid venous thromboembolism.

SUMMARY

Background The incidence of inflammatory bowel disease (IBD) increases, and thus is more common, in pregnant women. IBD is a risk factor for venous thromboembolism (VTE) but it is not clear whether IBD predisposes women to an excess risk of VTE during pregnancy and the postpartum period. Methods This was a nationwide population-based cohort study of all deliveries during 1980-2013 in Denmark, using data from two nationwide health registries: the Danish National Patient Registry and the Medical Birth Registry. We computed incidence rates (IRs) per 1000 person-years, and crude and adjusted relative risks (RRs) with 95% confidence intervals (CIs) for VTE during pregnancy and the first 12 postpartum weeks in women with and without IBD. Results We included 1 046 754 women with 1 978 701 deliveries. We identified 3465 VTE events during pregnancy and 1302 VTE events postpartum. The IR for VTE during pregnancy was 4.20 (95% CI, 2.83-5.58) in IBD patients and 2.41 (95% CI, 2.33-2.50) in women without IBD, corresponding to an RR of 1.72 (95% CI, 1.22-2.43). Adjustment for maternal age and smoking (pregnancies during 1991-2013) yielded an adjusted RR of 1.67 (95% CI, 1.15-2.41). IBD flare was associated with an RR of 2.64 (95% CI, 1.69-4.14) for VTE during pregnancy. The IR for postpartum VTE was 7.03 (95% CI, 3.87-10.20) among IBD patients and 2.88 (95% CI, 2.72-3.04) in women without IBD, corresponding to an adjusted RR of 2.10 (95% CI, 1.33-3.30). Conclusions IBD is a risk factor for VTE during pregnancy and postpartum.

Pre-admission use of glucocorticoids and 30-day mortality following colorectal cancer surgery: a population-based Danish cohort study

BACKGROUND

Previous studies indicate that pre-admission glucocorticoids increase the risk of perioperative complications.

AIM

To examine whether pre-admission use of glucocorticoids affects 30-day mortality after colorectal cancer (CRC) surgery.

METHODS

We conducted a nationwide population-based cohort study by linking Danish medical registries. All residents in Denmark who underwent CRC surgery from 2001 to 2011 were included. We characterised subjects who filled their most recent glucocorticoid prescription ≤90, 91-365 and >365 days before their surgery date as prevalent, recent and former users, respectively. Prevalent users were subgrouped into new (first-ever prescription ≤90 days before surgery date) and continuing users. We estimated 30-day cumulative mortality by the Kaplan-Meier method and corresponding mortality rate ratios (MRRs) using Cox proportional hazard regression, adjusting for potential confounders.

RESULTS

Of the 34 641 CRC patients included, 3966 (11.5%) had filled one or more prescriptions of glucocorticoids within the year before the surgery date. Thirty-day mortality among prevalent users of oral glucocorticoids was 15.0% vs. 7.3% among non-users [MRR = 1.28; 95% confidence interval (CI): 1.03, 1.58]. Among new users, the 30-day mortality was 17.8% (MRR = 1.92; 95% CI: 1.30, 2.83) while it was 14.2% among continuing users (MRR = 1.13; 95% CI: 0.88, 1.44). No associations were found for recent or former use of oral glucocorticoids nor for use of inhaled, intestinal-acting, and mixed glucocorticoids.

CONCLUSIONS

Prevalent use, particulary new use, of oral glucocorticoids was associated with markedly increased 30-day mortality after colorectal cancer surgery compared to patients not exposed to any glucocorticoids.

Does comorbidity interact with colorectal cancer to increase mortality? A nationwide population-based cohort study

BACKGROUND

It is unknown whether comorbidity interacts with colorectal cancer (CRC) to increase the rate of mortality beyond that explained by the independent effects of CRC and comorbid conditions.

METHODS

We conducted a cohort study (1995-2010) of all Danish CRC patients (n=56963), and five times as many persons from the general population (n=271670) matched by age, gender, and specific comorbidities. To analyse comorbidity, we used the Charlson Comorbidity Index (CCI) scores. We estimated standardised mortality rates per 1000 person-years, and calculated interaction contrasts as a measure of the excess mortality rate not explained by the independent effects of CRC or comorbidities.

RESULTS

Among CRC patients with a CCI score=1, the 0-1 year mortality rate was 415 out of 1000 person-years (95% confidence interval (CI): 401, 430) and the interaction accounted for 9.3% of this rate (interaction contrast=39 out of 1000 person-years, 95% CI: 22, 55). For patients with a CCI score of 4 or more, the interaction accounted for 34% of the mortality (interaction contrast=262 out of 1000 person-years, 95% CI: 215, 310). The interaction between CRC and comorbidities had limited influence on mortality beyond 1 year after diagnosis.

CONCLUSION

Successful treatment of the comorbidity is pivotal and may reduce the mortality attributable to comorbidity itself, and also the mortality attributable to the interaction.

Inverse melting and inverse freezing in a three-state spin-glass model with finite connectivity

The phase diagrams of the three-state Ghatak-Sherrington spin-glass (or random Blume-Capel) model are obtained in mean-field theory with replica symmetry in order to study the effects of a ferromagnetic bias and finite random connectivity in which each spin is connected to a finite number of other spins. It is shown that inverse melting from a ferromagnetic to a low-temperature paramagnetic phase may appear for small but finite disorder and that inverse freezing appears for large disorder. There can also be a continuous inverse ferromagnetic to spin-glass transition.

Use of systemic glucocorticoids and the risk of colorectal cancer

BACKGROUND

Systemic glucocorticoids are potent immunosuppressants, potentially facilitating carcinogenesis. Studies examining glucocorticoids and colorectal cancer risk are few.

AIM

To investigate the association between use of systemic glucocorticoids and colorectal cancer risk, both overall and by cancer stage (localised versus metastatic).

METHODS

We conducted a nested population-based case-control study in Northern Denmark (1.8 million people) using medical registries. The study included 14,158 patients with a first-time diagnosis of colorectal cancer from 1991 through 2010. Using risk set sampling, we identified 141,580 population controls, matched on age and gender. Logistic regression models were used to compute odds ratios (ORs) and 95% confidence intervals (CIs), adjusting for covariates.

RESULTS

Frequent use of systemic glucocorticoids (defined as >2 prescriptions) was not associated with overall colorectal cancer risk [adjusted OR (aOR) = 0.93 (95% CI: 0.85-1.00)], compared with never/rare use (≤2 prescriptions). Associations according to duration of use and doses (quartiles of cumulative prednisolone equivalents) were also near the null. Examining colorectal cancer by stage, no substantial associations were found between long-term use (>5 years) of high-dose (>5500 mg) systemic glucocorticoids and localised [aOR = 1.12 (95% CI: 0.81-1.55)] or metastatic [aOR = 0.82 (95% CI: 0.59-1.14)] cancer.

CONCLUSION

Despite immunological and metabolic effects of frequent use of systemic glucocorticoids, which would be expected to increase colorectal cancer risk, we found no substantial association between the two.

Prenatal exposure to acid-suppressive drugs and the risk of childhood asthma: a population-based Danish cohort study

BACKGROUND

Proton pump inhibitors (PPIs) may activate the immune system and cause asthma.

AIM

To investigate the association of prenatal exposure to PPIs and histamine 2-receptor antagonists (H2RAs) with risk of asthma.

METHODS

In this cohort study, 197,060 singletons born between 1996 and 2008 in northern Denmark were followed until the end of 2009. Data were obtained through Danish medical registries. Asthma in offspring was defined as at least two prescriptions of both a β-agonist and an inhaled glucocorticoid and/or a hospital diagnosis of asthma during the follow-up. Cox proportional-hazard regression was used to compute incidence rate ratios, adjusting for covariates.

RESULTS

A total of 2238 (1.1%) children were prenatally exposed to PPIs and 24,506 (12.4%) children developed asthma during follow-up (median follow-up = 6.8 years). The adjusted IRR (aIRR) of asthma associated with prenatal exposure to PPIs was 1.41 (95% confidence interval (CI): 1.27-1.56), compared with those unexposed. The association did not vary by trimester of exposure, and prenatal exposure to H2RAs was associated with similar increase in risk. The aIRR for maternal PPI and H2RA use in the year after, but not during pregnancy was 1.32 (95% CI: 1.20-1.46) and 1.13 (0.93-1.36), respectively, compared with non-use during and in the year after pregnancy.

CONCLUSIONS

Prenatal exposure to both PPIs and H2RAs was associated with an increased risk of asthma in our study. Because the observed association is not drug specific and also observed for maternal postnatal use it may be explained by a 'class effect' or maternal underlying condition.

Quality of ICD-10 colorectal cancer diagnosis codes in the Danish National Registry of Patients

This study examined the quality of International Classification of Diseases-10 colorectal cancer (CRC) diagnosis coding in the Danish National Registry of Patients (DNRP), using the Danish Cancer Registry (DCR) as a reference. We included all patients in Denmark with a CRC diagnosis in the DNRP and/or in the DCR from 2001 through 2006. Data quality was evaluated by estimating completeness and positive predictive value (PPV) of data in different subcategories of patients. We estimated mortality and date of diagnosis, to evaluate the effect of potential differences in data quality. Overall completeness of data in the DNRP for CRC was 93.4% [95% confidence interval (CI): 93.1-93.7] and the PPV was 88.9% (95% CI: 88.5-89.2). Completeness and PPV improved during the study period. However, the completeness of data for patients >75 years in the 2001-2003 period [88.8% (95% CI: 87.8-89.6)] was lower than average, and cancers in more unspecific locations and cancers in the colorectal junction also had lower estimates (below 90%). There were no differences in survival estimates in the DNRP compared to the DCR. In conclusion, this study shows high CRC data quality in the DNRP measured by completeness and PPV, except in a few subgroups.

Survival of invasive bladder cancer patients, 1998-2009; a central and northern Denmark population-based cohort study

Objective

Invasive bladder cancer (IBC) is a common urological malignancy accounting for 4%–5% of all cancers in Denmark. Our aim was to examine possible changes in short- and long-term survival of patients with IBC during 1998–2009.

Study design and setting

Data on all patients (N = 4032) with an incident diagnosis of IBC within a population of 1.8 million were retrieved from the Danish National Registry of Patients from 1998 to 2009. We computed survival after 1, 3, and 5 years, stratified by age and gender, and estimated mortality rate ratios (MRR) using Cox proportional hazard regression to compare mortality over time, controlling for age and gender. Data on tumor stage or histology were not included.

Results

During the study period, the annual numbers of incident IBC patients remained stable. The median age was 74 years in each of the four 3-year periods in the study. The survival was relatively stable during the first three periods, whilst data from the last period showed modest improvement. The overall 1-year survival increased from 68% in 1998–2000 to 70% in 2007–2009, corresponding to an age and gender adjusted MRR of 0.89 (95% confidence interval [CI] 0.76–1.03). The 3- and 5-year survival was predicted to increase from 44% to 49% and from 35% to 40% respectively. This corresponded to a 3-year age and gender adjusted MRR of 0.87 (95% CI 0.77–0.98) and a 5-year MRR of 0.88 (95% CI 0.79–0.99). The 1-, 3-, and 5-year survival increased for men in all age groups (<70 years, 70–79 years, ≥80 years) and in women only in the 70–79-year age group.

Conclusion

The survival of IBC patients increased slightly in northern and central Denmark in the 1998–2009 period.

Phase transitions in the three-state Ising spin-glass model with finite connectivity

The statistical mechanics of a two-state Ising spin-glass model with finite random connectivity, in which each site is connected to a finite number of other sites, is extended in this work within the replica technique to study the phase transitions in the three-state Ghatak-Sherrington (or random Blume-Capel) model of a spin glass with a crystal-field term. The replica symmetry ansatz for the order function is expressed in terms of a two-dimensional effective-field distribution, which is determined numerically by means of a population dynamics procedure. Phase diagrams are obtained exhibiting phase boundaries that have a reentrance with both a continuous and a genuine first-order transition with a discontinuity in the entropy. This may be seen as "inverse freezing," which has been studied extensively lately, as a process either with or without exchange of latent heat.

Multistability in networks of Hindmarsh-Rose neurons

We investigate the dynamical states of a two-dimensional network of Hindmarsh-Rose spiking neurons, in the vicinity of the current threshold where the single neuron becomes active. Each neuron is electrically coupled with neurons in its close neighborhood. The existence of multistable synchronization states is established and discussed. We also show that, provided adequate initial conditions, the collective behavior is able to keep the network in activity, even for current values far below the activity threshold of the single neuron. A phase diagram of the different network states is presented for a large interval of the coupling-current parameter space.

Periodicity and chaos in electrically coupled Hindmarsh-Rose neurons

The Hindmarsh-Rose (HR) system of equations is a model that captures the essential of the spiking activity of biological neurons. In this work we present an exploratory numerical study of the time activities of two HR neurons interacting through electrical synapses. The knowledge of this simple system is a first step towards the understanding of the cooperative behavior of large neural assemblies. Several periodic and chaotic attractors where identified, as the coupling strength is increased from zero until the perfect synchronization regime. In addition to the known phase locking synchronization at weak coupling, electrical synapses also allow for both in-phase and antiphase synchronization from moderate to strong coupling. A regime where the system changes apparently randomly between in-phase and antiphase locking evolves to a bistability regime, where both in-phase and antiphase periodic attractors are locally stable. At the strong coupling regime in-phase chaotic evolution dominates, but windows with complex periodic behavior are also present.

Time evolution of the extremely diluted Blume-Emery-Griffiths neural network

A study of the time evolution and a stability analysis of the phases in the extremely diluted Blume-Emery-Griffiths neural network model are shown to yield new phase diagrams in which fluctuation retrieval may drive pattern retrieval. It is shown that saddle-point solutions associated with fluctuation overlaps slow down the flow of the network states towards the retrieval fixed points. A comparison of the performance with other three-state networks is also presented.

Retrieval behavior and thermodynamic properties of symmetrically diluted Q-Ising neural networks

The retrieval behavior and thermodynamic properties of symmetrically diluted Q-Ising neural networks are derived and studied in replica-symmetric mean-field theory generalizing earlier works on either the fully connected or the symmetrical extremely diluted network. Capacity-gain parameter phase diagrams are obtained for the Q=3, Q=4, and Q=infinity state networks with uniformly distributed patterns of low activity in order to search for the effects of a gradual dilution of the synapses. It is shown that enlarged regions of continuous changeover into a region of optimal performance are obtained for finite stochastic noise and small but finite connectivity. The de Almeida-Thouless lines of stability are obtained for arbitrary connectivity, and the resulting phase diagrams are used to draw conclusions on the behavior of symmetrically diluted networks with other pattern distributions of either high or low activity.

Categorization in fully connected multistate neural network models

The categorization ability of fully connected neural network models, with either discrete or continuous Q-state units, is studied in this work in replica symmetric mean-field theory. Hierarchically correlated multistate patterns in a two level structure of ancestors and descendents (examples) are embedded in the network and the categorization task consists in recognizing the ancestors when the network is trained exclusively with their descendents. Explicit results for the dependence of the equilibrium properties of a Q=3-state model and a Q=infinity-state model are obtained in the form of phase diagrams and categorization curves. A strong improvement of the categorization ability is found when the network is trained with examples of low activity. The categorization ability is found to be robust to finite threshold and synaptic noise. The Almeida-Thouless lines that limit the validity of the replica-symmetric results, are also obtained.

Coupling of low-frequency modes with the complex Ginzburg-Landau equation: Generalized Zakharov equations

In this paper we introduce and examine a generalization of the complex Ginzburg-Landau equation (CGLE) where the self-interaction contained in the cubic term is replaced by a coupling involving the original field and a low-frequency one. New instabilities arise and a radically new asymptotic dynamical behavior emerges displaying defect turbulence over wide regions of the parameter space.

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After 1933 many scientists and university teachers were obliged to relinquish their posts in the universities of Germany because of national-socialist laws. Organizations-in-aid like the Academic Assistance Council in Great Britain tried to 'defend science and learning' raising funds and finding new openings for the expelled academics. But as immigration laws were tight and jobs were scarce in the host countries the AAC and the other organizations had to select the most qualified from among the applicants for support. -- The questions the article tries to answer are: What kind of criteria were applied in this selection? Who were the experts? How were the placements made? How did the applicants react to the decisions? Taking for example the AAC, it examines measures to assist a group of scientists who, having tried to settle down in England, finally emigrated to Turkey.