[Clinical observation of coblation assisted transoral microsurgery for the treatment of oral and oropharygneal malignancy]

Objective:To evaluate the feasibility and effectiveness of coblation assisted transoral surgery for the treatment of oral and oropharyngeal malignancy. Method:19 patients who suffered from oral or oropharyngeal malignant tumors underwent coblation assisted transoral surgery from August 2008 to August 2017 were studied. According to the tumor sites and pathological results, there were four oral squamous cell carcinoma (SCC) (two tongue carcinoma and two mouth floor carcinoma), eleven oropharygneal SCC (five tonsillar carcinoma, four soft palate carcinoma, one tongue base cartinama and one multiple carcinoma invading both soft palatine and hypopharynx), and four lymphatic and hematopoietic malignancies (three tonsillar tumors and one tumor invading both tonsil and tongue base). According to AJCC guideline, the stages of four oral SCC were T₁N₀M₀, T₁N₂M₀, T₂N₁M₀, and T₂N₂M₀ respectively; while the stages of eleven orophygneal SCC were T₁N₀M₀ for 5 patients, T₂N₀M₀ for 4 patients, T₂N₁M₀ for one patient, and T₂N₂M₀ for one patient respectively. Result:Among the 19 patients studied, concurrent neck dissections and tracheotomies were performed in six and four patients respectively. For all the transoral procedures, the blood loss could be controlled within 20 ml, while the operative time were controlled within two hours. 13 patients started oral feeding the day they were operated on. All of the four patients who underwent the tracheotomy could be decannulated successfully after surgery. Four patients diagnosed as lymphatic and hematopoietic malignancies turned to hematology department for further treatments. For the remaining 15 SCC patients, 14 were followed up successfully with one loss to follow-up: the follow up time ranged from 6 to 108 months, during these times, one patient with multiple carcinomas invading the soft palate and hypopharynx had developed new carcinomas located in contralateral hypopharynx and esophagus and had the metastasis in cervical lymph nodes 5 months after surgery, another patient with soft palate carcinoma had the metastasis in cervical lymph nodes 18 months after surgery. Two patients died because of intracranial hemorrhage and cardiovascular event 5 and 12 months after surgery respectively. The three years' tumor free survival and overall survival rates calculated by Kaplan-Meier method were 75.0% and 77.9% respectively. All patients had no severe dysfunctions for swallow, speech and breathing related to the surgery. Conclusion:Radiofrenquency coblation assisted transoral surgery for oral and oropharygneal carcinoma has definite therapeutic effect. Most cases can avoid open surgery and tracheotomy.The advantages are blood control, simplifing surgery,shortening operational time,faster recovery, lower incidence of complications and better preservation of organ function.

Dijet imbalance measurements in Au+Au and pp collisions at sqrt[s_{NN}]=200 GeV at STAR

We report the first dijet transverse momentum asymmetry measurements from Au+Au and pp collisions at RHIC. The two highest-energy back-to-back jets reconstructed from fragments with transverse momenta above 2  GeV/c display a significantly higher momentum imbalance in heavy-ion collisions than in the pp reference. When reexamined with correlated soft particles included, we observe that these dijets then exhibit a unique new feature-momentum balance is restored to that observed in pp for a jet resolution parameter of R=0.4, while rebalancing is not attained with a smaller value of R=0.2.

[Minor salivary duct carcinoma of the larynx: a case report]

Salivary duct carcinoma SDC is a rare disease, especially in the larynx. From the pathology point of view, SDC histomorphology is very similar to breast ductal carcinoma. From the immunohistochemistry, epithelial antibodies are positive, but the SMA is negative. From the review of papers, total resection is the first choice for the treatment, but the local recurrence and distant metastasis are the main influence factors for survival rate. Now we still lack the clinical experience for such disease.

High-resolution and multi-range particle separation by microscopic vibration in an optofluidic chip

An optofluidic chip is demonstrated in experiments for high-resolution and multi-range particle separation through the optically-induced microscopic vibration effect, where nanoparticles are trapped in loosely overdamped optical potential wells created with combined optical and fluidic constraints. It is the first demonstration of separating single nanoparticles with diameters ranging from 60 to 100 nm with a resolution of 10 nm. Nanoparticles vibrate with an amplitude of 3-7 μm in the loosely overdamped potential wells in the microchannel. The proposed optofluidic device is capable of high-resolution particle separation at both nanoscale and microscale without reconfiguring the device. The separation of bacteria from other larger cells is accomplished using the same chip and operation conditions. The unique trapping mechanism and the superb performance in high-resolution and multi-range particle separation of the proposed optofluidic chip promise great potential for a diverse range of biomedical applications.

Measurement of D^{0} Azimuthal Anisotropy at Midrapidity in Au+Au Collisions at sqrt[s_{NN}]=200 GeV

We report the first measurement of the elliptic anisotropy (v_{2}) of the charm meson D^{0} at midrapidity (|y|<1) in Au+Au collisions at sqrt[s_{NN}]=200  GeV. The measurement was conducted by the STAR experiment at RHIC utilizing a new high-resolution silicon tracker. The measured D^{0} v_{2} in 0%-80% centrality Au+Au collisions can be described by a viscous hydrodynamic calculation for a transverse momentum (p_{T}) of less than 4  GeV/c. The D^{0} v_{2} as a function of transverse kinetic energy (m_{T}-m_{0}, where m_{T}=sqrt[p_{T}^{2}+m_{0}^{2}]) is consistent with that of light mesons in 10%-40% centrality Au+Au collisions. These results suggest that charm quarks have achieved local thermal equilibrium with the medium created in such collisions. Several theoretical models, with the temperature-dependent, dimensionless charm spatial diffusion coefficient (2πTD_{s}) in the range of ∼2-12, are able to simultaneously reproduce our D^{0} v_{2} result and our previously published results for the D^{0} nuclear modification factor.

[The multicenter study on the registration and follow-up of low anticoagulation therapy for the heart valve operation in China]

OBJECTIVE

To investigate the optimal anticoagulation methods and monitoring strategy for Chinese patients undergoing heart valve replacement, which is potentially quite different from western populations.

METHODS

In this multicenter prospective cohort study, the anticoagulation and monitoring strategy data was acquired from 25 773 in-hospital patients in 35 medical centers and 20 519 patients in outpatient clinic in 11 medical centers from January 1st, 2011 to December 31th, 2015.

RESULTS

As for in-hospital patients, mean age of study population was (48.6±11.2) years old; main etiology of valve pathology was rheumatic (87.5%) origin among study cohort; 94.8% of study population received mechanical valve implantation; international normalized ratio (INR) monitoring (in all the study centers) and low-intensity anticoagulation strategy (31 hospitals chose target INR range of 1.5-2.5, and actual values of INR among 89.2% of 100 069 in-hospital monitoring samples were 1.5-2.5), with mean actual INR values of 1.84±0.53, and warfarin dosage of (2.82±0.93) mg/d were widely adopted among the study centers; strategies of in-hospital warfarin administration were similar in all the study centers; complication rates of low-intensity anticoagulation strategy were low in severe hemorrhage (0.02%), thrombosis (0.05%), and thromboembolism (0.05%) events, without anticoagulation-related death.As for 18 974 outpatient clinic patients, the follow-up rate was 92.47%, with a total of 30 012 patient-years (Pty). Anticoagulation-related morbidity and mortality rates were 0.67% and 0.15% Pty; major hemorrhage morbidity and mortality rates were 0.25% and 0.13% Pty; thromboembolism morbidity and mortality rates were 0.45% and 0.03% Pty.The mean dosage of warfarin daily dosage was (2.85±1.23) mg/d and INR value was 1.82±0.57.No significant regional difference in the intensity of anticoagulation therapy was noted during the study.

CONCLUSIONS

INR can be used as a normalized indicator for intensity of anticoagulation therapy in China.The optimal anticoagulation intensity with INR range from 1.5 to 2.5 is safe and effective for Chinese patients with heart valve replacement, and there is no significant regional difference in the intensity of anticoagulation therapy.

Charge-Dependent Directed Flow in Cu+Au Collisions at sqrt[s_{NN}]=200 GeV

We present the first measurement of charge-dependent directed flow in Cu+Au collisions at sqrt[s_{NN}]=200  GeV. The results are presented as a function of the particle transverse momentum and pseudorapidity for different centralities. A finite difference between the directed flow of positive and negative charged particles is observed that qualitatively agrees with the expectations from the effects of the initial strong electric field between two colliding ions with different nuclear charges. The measured difference in directed flow is much smaller than that obtained from the parton-hadron-string-dynamics model, which suggests that most of the electric charges, i.e., quarks and antiquarks, have not yet been created during the lifetime of the strong electric field, which is of the order of, or less than, 1  fm/c.

Association of growth factor receptor-bound protein 10 gene polymorphism with superovulation traits in Changbaishan black cattle

The application of assisted reproductive technology in animal production benefits the economy and conservation of biological resources. Single nucleotide polymorphism (SNPs) was used as predictive markers for breeding and reproduction. In the present study, we examined the association between a SNP of the grb10 gene and superovulation traits in cattle. Sequencing results indicated a point mutation and statistical analysis showed a significant association of the mutation with superovulation traits. The high number of embryos collected from the heterozygotes suggested that the mutation in the grb10 gene exerted a significant effect on the number of embryos recovered although the quality was not affected. The grb10 gene may serve as a useful biomarker for donor selection.

Association between polymorphisms in the promoter region of pri-miR-34b/c and risk of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a major cause of cancer-related deaths worldwide. MicroRNA-34 (miR-34) gene plays a key role in altering the apoptotic cycle and pathways of downstream cells, and therefore influences carcinogenesis. In this case-control study, we assessed the role of the pri-miR-34b/c rs4938723 polymorphism in HCC risk. The pri-miR-34b/c polymorphic genotype was determined in 286 patients with HCC and 572 controls using polymerase chain reaction-restriction fragment length polymorphism. The male gender (X² = 12.95, P < 0.001), regular alcohol consumption (X² = 16.81, P < 0.001), and a family history of cancer (X² = 11.88, P = 0.001) were associated with HCC risk. However, the age (t = 1.19, P = 0.12) and tobacco smoking habit (X² = 0.64, P = 0.42) of HCC patients were comparable to those of the controls. The TC (adjusted OR = 1.46, 95%CI = 1.06-2.01) and CC (adjusted OR = 3.07, 95%CI = 1.77-5.34) genotypes of pri-miR-34b/c rs4938723 were correlated with a higher risk of HCC compared to the TT genotype. Moreover, the TC+CC genotype was correlated with an increased risk of HCC compared to the TT genotype (adjusted OR = 1.64, 95%CI = 1.21-2.22). In the recessive model, the CC genotype of pri-miR-34b/c rs4938723 was significantly correlated with an elevated risk of HCC compared to the TT+TC genotype (adjusted OR = 2.50, 95%CI = 1.49-4.22). Further large-scale and multi-center studies are required to confirm these results.

[The distribution characteristics of etiology of chronic cough in Lanzhou]

OBJECTIVE

To explore the distribution characteristics of etiology and clinical feature of chronic cough in Lanzhou.

METHODS

Based on the guidelines of the diagnostic process of chronic cough in China, data of medical history and physical examinations were collected, and chest X-ray, pulmonary function plus airway hyperresponsiveness, induced sputum eosinophils, sinus X-ray or CT, 24 h esophageal pH monitoring, chest high-resolution CT and bronchoscopy were performed accordingly for outpatients with chronic cough. The cause of chronic cough was identified by the test results and treatment response. The results were compared with those reported previously in other areas of China.

RESULTS

A total of 173 patients with completed data were collected, including 90 males and 83 females.The causes were as follows: 45 cases (26.01%) of cough variant asthma, 35 (20.23%) upper airway cough syndrome, 20 (11.56%) allergic cough, 17 (9.83%) chronic pharyngitis, 14 (8.09%) gastroesophageal reflux, 14 (8.09%)postinfectious, 13 (7.51%) eosinophilic bronchitis, 8 (4.62%) chronic bronchitis, 4 (2.31%) cough associated with ACEI, 3 (1.73%) bronchial tuberculosis, 2 (1.16%) pulmonary fibrosis and bronchiectasis repectively. The causes of the remaining 14 patients (8.09%)were unknown. The causes of chronic cough were identified in 159 patients (91.91%), of which 141 (88.68%) with a single cause and 18(11.32%)with more than 2 etiological factors.The percentage of cough variant asthma in our series was significantly higher than that reported in Guangzhou (13.6%, χ(2)=5.60, P=0.018, P<0.05), but lower than that reported in Shenyang (39.4%, χ(2)=7.91, P=0, 004, P<0.01). The percentage of allergic cough was higher than that reported in Beijing (3.3%, χ(2)=6.66, P=0.010, P<0.05), and that of eosinophilic bronchitis was lower than those reported in Guangzhou(22.4%, χ(2)=22.38, P=0.000, P<0.01) and Shenyang (12.5%, χ(2)=8.09, P=0.005, P<0.01). The percentage of esophageal reflux cough was lower than that reported in Beijing (20.3%, χ(2)=9.40, P=0.002, P<0.01) but higher than that reported in Shenyang (1.9%, χ(2)=3.98, P=0.036, P<0.05).

CONCLUSION

In Lanzhou, cough variant asthma, upper airway cough syndrome, allergic cough, chronic pharyngitis and gastroesophageal reflux were the main causes of chronic cough, and the etiological distribution was different from Guangzhou, Beijing, Shenyang and other areas.

A Comparison of Traditional Digital Blocks and Single Subcutaneous Palmar Injection Blocks at the Base of the Finger and a Meta-Analysis of the Digital Block Trials

A randomised, double-blinded, controlled trial was performed to compare traditional digital blocks with single subcutaneous palmar injection blocks at the base of the finger. A search for randomised controlled trials of digital blocks through MEDLINE, EMBASE, Cochrane Controlled Trials Register and CBM was conducted and a meta-analysis including the current trial was performed. The current trial showed no difference between traditional digital blocks and single subcutaneous palmar injection bocks at the base of the finger in respect of injection pain and time to anaesthesia. The meta-analysis suggests that traditional digital blocks and single subcutaneous palmar injection blocks are similar with regard to injection pain and are less painful than the transthecal digital block. The palmar techniques, including single subcutaneous palmar block and transthecal block, carry a risk of not anaesthetising the dorsum of the digit adequately, particularly the dorsum of the thumb and the proximal phalanx of the fingers.

Correction: Optofluidic lens with low spherical and low field curvature aberrations

Correction for 'Optofluidic lens with low spherical and low field curvature aberrations' by H. T. Zhao et al., Lab Chip, 2016, 16, 1617-1624.

Microstructures, mechanical properties and corrosion resistances of extruded Mg-Zn-Ca-xCe/La alloys

Magnesium alloys are considered as good candidates for biomedical applications, the influence of Ce/La microalloying on the microstructure, mechanical property and corrosion performance of extruded Mg-5.3Zn-0.6Ca (wt%) alloy has been investigated in the current study. After Ce/La addition, the conventional Ca2Mg6Zn3 phases are gradually replaced by new Mg-Zn-Ce/La-(Ca) phases (T1'), which can effectively divide the Ca2Mg6Zn3 phase. The Ca2Mg6Zn3/T1' structure in Mg-Zn-Ca-0.5Ce/La alloy is favorably broken into small particles during the extrusion, resulting in an obvious refinement of secondary phase. The dynamic recrystallized grain size is dramatically decreased after 0.5Ce/La addition, and the tensile yield strength is improved, while further addition reverses the effect, due to the grain coarsening. However, the corrosion resistance of extruded Mg-Zn-Ca alloy deteriorates after Ce/La addition, because the diameter of secondary phase particle is remarkably decreased, which increases the amount of cathodic sites and accelerates the galvanic corrosion process.

Optofluidic lens with low spherical and low field curvature aberrations

This paper reports an optofluidic lens with low spherical and low field curvature aberrations through the desired refractive index profile by precisely controlling the mixing between ethylene glycol and deionized water in an optofluidic chip. The experimental results demonstrate that the spherical aberration is reduced to 19.5 μm and the full width at half maximum of the focal point is 7.8 μm with a wide divergence angle of 35 degrees. In addition, the optofluidic lens can focus light at different off-axis positions on the focal plane with Δx' < 6.8 μm and at opposite transverse positions with |Δy - Δy'| < 5.7 μm. This is the first demonstration of a special optofluidic lens that significantly reduces both the spherical and field curvature aberrations, which enhances the focusing power and facilitates multiple light source illumination using a single lens. It is anticipated to have high potential for applications such as on-chip light manipulation, sample illumination and multiplexed detection.

AMFR gene silencing inhibits the differentiation of porcine preadipocytes

Our study clarifies the role of the autocrine motility factor receptor (AMFR) gene in porcine preadipocyte differentiation. AMFR-siRNA was transfected into porcine preadipocytes and the preadipocytes were induced to differentiation. Subsequently, qRT-PCR was conducted to examine changes in mRNA expression of a series of genes in porcine preadipocytes, including AMFR, sterol-regulatory element-binding protein-1a (SREBP1a), SREBP2, insulin-induced gene 1 (Insig1), and Insig2. Expression changes in the mRNA of genes regulating adipocyte differentiation were also analyzed using qRT-PCR, including peroxisome proliferator-activated receptor gamma (PPARγ), CCAAT/enhancer-binding protein alpha (C/EBPα), and Kruppel-like factor 2 (KLF2). Western blot analysis was conducted to examine the changes in AMFR protein expression in porcine preadipocytes. Additionally, morphological changes in differentiated porcine preadipocytes were examined by oil red O staining, and changes in optical density (OD) values were measured using an ultraviolet spectrophotometer. At 24 h after transfection with AMFR-siRNA, AMFR mRNA expression significantly reduced (P < 0.01), and AMFR protein expression markedly decreased (P < 0.05). The mRNA expression of SREBP1a, SREBP2, Insig1, and C/EBPα was significantly reduced (P < 0.01), whereas the expression of KLF2 mRNA was significantly elevated (P < 0.01). After induction of preadipocyte differentiation, the number of lipid droplets decreased in the AMFR-silenced group, and the OD value markedly reduced (P < 0.05). In addition, the expression of C/EBPα mRNA significantly decreased (P < 0.05), whereas the expression of KLF2 mRNA considerably increased (P < 0.05). Taken together, silencing of the AMFR gene inhibits the differentiation of porcine preadipocytes.

Measurement of the Transverse Single-Spin Asymmetry in p^{↑}+p→W^{±}/Z^{0} at RHIC

We present the measurement of the transverse single-spin asymmetry of weak boson production in transversely polarized proton-proton collisions at sqrt[s]=500  GeV by the STAR experiment at RHIC. The measured observable is sensitive to the Sivers function, one of the transverse-momentum-dependent parton distribution functions, which is predicted to have the opposite sign in proton-proton collisions from that observed in deep inelastic lepton-proton scattering. These data provide the first experimental investigation of the nonuniversality of the Sivers function, fundamental to our understanding of QCD.

Beam Energy Dependence of the Third Harmonic of Azimuthal Correlations in Au+Au Collisions at RHIC

We present results from a harmonic decomposition of two-particle azimuthal correlations measured with the STAR detector in Au+Au collisions for energies ranging from sqrt[s_{NN}]=7.7 to 200 GeV. The third harmonic v_{3}^{2}{2}=⟨cos3(ϕ_{1}-ϕ_{2})⟩, where ϕ_{1}-ϕ_{2} is the angular difference in azimuth, is studied as a function of the pseudorapidity difference between particle pairs Δη=η_{1}-η_{2}. Nonzero v_{3}^{2}{2} is directly related to the previously observed large-Δη narrow-Δϕ ridge correlations and has been shown in models to be sensitive to the existence of a low viscosity quark gluon plasma phase. For sufficiently central collisions, v_{3}^{2}{2} persist down to an energy of 7.7 GeV, suggesting that quark gluon plasma may be created even in these low energy collisions. In peripheral collisions at these low energies, however, v_{3}^{2}{2} is consistent with zero. When scaled by the pseudorapidity density of charged-particle multiplicity per participating nucleon pair, v_{3}^{2}{2} for central collisions shows a minimum near sqrt[s_{NN}]=20  GeV.

Misdiagnosis of primary hepatic marginal zone B cell lymphoma of mucosa-associated lymphoid tissue type, a case report

Background

Extra-nodal marginal zone B cell lymphoma of mucosa-associated lymphoid tissue originating in the liver is less common.

Case presentation

We described the clinical presentation, immunohistochemistry, and immunophenotypes of this lymphoma, which was misdiagnosed with tiny hepatic carcinoma in a 44-year-old woman with hepatitis C; the patient underwent left lateral sectionectomy. The immunophenotype identified the most of the lymphoid cells as positive CD20, CD34, Ki67, CD3, CD4, CD79a, CD45RO, MUM-1, and CD5 and negative CD10, CD15, CD30, ACT, CK, CRO, DES, and HMB45. The diagnosis of primary hepatic mucosa-associated lymphoid tissue (MALT) was made by histology after surgery; the patient went through the excellent recovery with no chemotherapy and is disease free for 27 months.

Conclusions

Primary hepatic MALT is less common with incidental finding; local resection is beneficial due to its oncological indolence.

Centrality and Transverse Momentum Dependence of Elliptic Flow of Multistrange Hadrons and ϕ Meson in Au+Au Collisions at √[sNN]=200 GeV

We present high precision measurements of elliptic flow near midrapidity (|y|<1.0) for multistrange hadrons and ϕ meson as a function of centrality and transverse momentum in Au+Au collisions at center of mass energy √[sNN]=200  GeV. We observe that the transverse momentum dependence of ϕ and Ω v2 is similar to that of π and p, respectively, which may indicate that the heavier strange quark flows as strongly as the lighter up and down quarks. This observation constitutes a clear piece of evidence for the development of partonic collectivity in heavy-ion collisions at the top RHIC energy. Number of constituent quark scaling is found to hold within statistical uncertainty for both 0%-30% and 30%-80% collision centrality. There is an indication of the breakdown of previously observed mass ordering between ϕ and proton v2 at low transverse momentum in the 0%-30% centrality range, possibly indicating late hadronic interactions affecting the proton v2.

Expression pattern of JMJD1C in oocytes and its impact on early embryonic development

Cell reprogramming mediated by histone methylation and demethylation is crucial for the activation of the embryonic genome in early embryonic development. In this study, we employed quantitative real-time polymerase chain reaction (qRT-PCR) to detect mRNA levels and expression patterns of all known histone demethylases in early germinal vesicle stage and in vitro-matured metaphase II (MII) oocytes (which are commonly used as donor cells for nuclear transfer). On screening, the Jumonji domain containing 1C (JMJD1C) gene had the highest level of expression and hence was used for subsequent experiments. We also found that JMJD1C was primarily expressed in the nucleus and showed relatively high levels of expression at the 2-cell, 4-cell, 8-cell, 16-cell, morula, and blastocyst stages of embryos developed from MII oocytes fertilized in vitro. Further, we knocked down the JMJD1C gene in MII oocytes using siRNA and monitored the cleavage of zygotes and development of early embryos after in vitro fertilization. The results showed that the zygote cleavage and blastocyst rates of the transfection group were reduced by 57.1 ± 0.07 and 50 ± 0.01% respectively, which were significantly lower than those of the negative control group (P < 0.05). These data suggest that JMJD1C plays a key role in the normal development of early bovine embryos. Our results also provide a theoretical basis for the investigation of the role and molecular mechanism of histone demethylation in the early development of bovine embryos.

Observation of Transverse Spin-Dependent Azimuthal Correlations of Charged Pion Pairs in p^{↑}+p at sqrt[s]=200 GeV

We report the observation of transverse polarization-dependent azimuthal correlations in charged pion pair production with the STAR experiment in p^{↑}+p collisions at RHIC. These correlations directly probe quark transversity distributions. We measure signals in excess of 5 standard deviations at high transverse momenta, at high pseudorapidities η>0.5, and for pair masses around the mass of the ρ meson. This is the first direct transversity measurement in p+p collisions.

Azimuthal Anisotropy in U+U and Au+Au Collisions at RHIC

Collisions between prolate uranium nuclei are used to study how particle production and azimuthal anisotropies depend on initial geometry in heavy-ion collisions. We report the two- and four-particle cumulants, v_{2}{2} and v_{2}{4}, for charged hadrons from U+U collisions at sqrt[s_{NN}]=193  GeV and Au+Au collisions at sqrt[s_{NN}]=200  GeV. Nearly fully overlapping collisions are selected based on the energy deposited by spectators in zero degree calorimeters (ZDCs). Within this sample, the observed dependence of v_{2}{2} on multiplicity demonstrates that ZDC information combined with multiplicity can preferentially select different overlap configurations in U+U collisions. We also show that v_{2} vs multiplicity can be better described by models, such as gluon saturation or quark participant models, that eliminate the dependence of the multiplicity on the number of binary nucleon-nucleon collisions.