Small Break Research Articles

Investigation of the small break conditions in the primary circuit of a VVER-1000 reactor*

Modes with violation of the reactor plant cooling conditions on the primary circuit side of a VVER reactor were simulated using the TRAC-PD2 and Open FOAM thermohydraulic codes (TRAC-PD2 1981, OpenFOAM User Guide Version 1.6. 2009, OpenFOAM Programmer’s Guide Version 1.6. 2009) based on energy and mass conservation equations for the three-dimensional unsteady flow of a two-phase mixture. Coupled simulation of the dynamics of neutronic and thermohydraulic processes (TRAC-PD2 1981, OpenFOAM User Guide Version 1.6. 2009, OpenFOAM Programmer’s Guide Version 1.6. 2009, Bolshagin et al. 2009, Galanin 1971, Weinberg and Wigner 1961, Ovchinnikov and Semenov 1988, Report LA-UR-03-1987) aims to improve the qualitative understanding and the quantitative presentation of their effects on safety. Investigating these modes using the above thermohydraulic codes makes it possible to analyze the course of transients and certain emergency processes without using the industrial testing method, this providing the basis for solving the problems of ensuring the reliability, operational safety and efficiency of nuclear power plants. A modern nuclear reactor is a complex system studying and calculating which requires more than the use of simple theoretical models. Thermohydraulic calculations are an essential part of most engineering and technological development works in nuclear power. Since, in conditions of an NPP, no technologically conventional way can be used to verify and update the results and findings of an a priori analysis on the basis of commercial tests, investigations based on codes are used in some cases as the tools to study and predict the parameters of thermohydraulic processes in the reactor’s circulation circuit. The main purpose of the study is to calculate and investigate, based on codes, modes with violation of the reactor plant cooling conditions on the primary circuit side of a VVER reactor in order to determine if calculated parameters conform to the acceptance criteria established by regulatory documents.

CFD investigation on reverse flow characteristics in U-tubes under two-phase natural circulation

During the small break loss of coolant accident (SBLOCA) in a pressurized water reactor (PWR), single and two-phase natural circulations (NCs) as well as reflux condensation can be the three major flow modes in the primary side to remove the residual core heat. The performance of U-tube steam generators (UTSGs) during the accident is of great significance for the reactor safety and integrity. However, flow behaviors in UTSG parallel U-tubes are considerably complicated and the reverse flow phenomenon may occur during both the single and two-phase NCs. Despite the rich researches on the phenomenon occurring under the single-phase NC, studies concerning that under the two-phase NC are still quite scarce. In this paper, the vapor-liquid two-phase flow condensed in the U-tube is numerically simulated using the computational fluid dynamics (CFD) method. The distribution of vapor volume fraction αg in the U-tube is investigated and analyzed. It is shown that a negative slope region obviously exists in the curve of pressure drop versus mass flow rate, and two-phase flow excursion can occur if the mass flow rate reduces to a critical value, namely the critical mass flow rate Mc. Afterwards, some influence factors on αg and Mc are numerically studied, which include the inlet vapor volume fraction, the bubble diameter, the inlet slip ratio, the U-tube wall temperature and the primary side pressure. The results can provide references for the long-term core cooling during a SBLOCA and the optimization design of SGs.

Virtual contributions from D⁎(2007)0 and D⁎(2010)± in the B → Dπh decays

We study the quasi-two-body decays B→D⁎h→Dπh with h=(π,K) in the perturbative QCD approach and focus on the virtual contributions from the off-shell D⁎(2007)0 and D⁎(2010)± in the four measured decays B¯0→D0π+π−, B¯0→D0π+K−, B−→D+π−π− and B−→D+π−K−. For the B¯0→D⁎+π−→D0π+π− and B¯0→D⁎+K−→D0π+K− decays, their branching fractions concentrate in a very small region of mD0π+ near D⁎+ pole mass, and the virtual contributions from D⁎+, in the region mD0π+>2.1 GeV, are about 5% of the corresponding quasi-two-body results. We define two ratios RD⁎+ and RD⁎0, from which we conclude that the flavor-SU(3) symmetry will be maintained for the B→D⁎h→Dπh decays with very small breaking at any physical value of the mDπ. The B−→D⁎0π−→D0π0π− and B−→D⁎0K−→D0π0K− decays can be employed as a constraint for the D⁎0 decay width, with preferred values consistent with previous theoretical predictions for this quantity.

Overall thermal-hydraulic behavior in an SBO test using HSIT in the ATLAS facility

A station blackout test called SBO-HSIT (Station Blackout-Hybrid Safety Injection Tank) was performed at the ATLAS (Advanced Thermal-Hydraulic Test Loop for Accident Simulation) facility. An overall review of the SBO-HSIT test was performed, including comparisons with a previous SBO test and small break loss-of-coolant accident (SBLOCA) tests relating to similar thermal-hydraulic behavior. The decay heat release in the SBO-HSIT test was carried out through the main steam safety valves (MSSVs) until the steam generator (SG) dryout, and after that by blowdown through the power operated safety relief valve (POSRV). Most of the major thermal-hydraulic behavior happened during this blowdown period. It is noteworthy that the reactor pressure vessel (RPV) took charge of the pressurizer (PZR) function after it reached a saturated condition and then the PZR became a simple buffer tank along the POSRV flow path. This seemed to hinder the PZR inventory from being drained to the primary circuits. Loop flows showed unstable conditions under a slightly subcooled condition of the upper plenum of RPV (RPV-UP) region, and the natural circulation was broken after the SG U-tube became empty. Loop seal clearings (LSCs) occurred twice during the test and the downcomer (DC) water levels maintained significantly higher values compared to the SBLOCA cases. Pseudo differential pressure (DP) values appeared in some pressure balance lines (PBLs) due to the existence of void in the PBLs, and the injection flowrates from the HSITs tended to increase after the intrusion of voids into the corresponding PBL. Quite a large amount of emergency core cooling water (ECCW) inventory remained in the closed HSITs in the test. Finally, a core heatup occurred at low core water level despite a rather large amount of PZR inventory, whose drainage was hindered by the pressurizer function of the RPV, and of HSITs inventories, whose drainage was interrupted by the closure logic for HSITs, respectively.

Microscale wave breaking in stratified air-water pipe flow

We perform an experimental analysis of two-phase stratified wavy pipe flow, with the aim to detect and quantify the effect of small scale wave breaking. Particle image velocimetry is employed to analyze the velocity fields below individual waves, and a threshold for the vorticity on the leeward side of the crest is used to assess active wave breaking. Keeping the liquid flow rate constant, we analyze five experimental cases with increasing gas flow rates. The cases span the flow map from when first interfacial waves are observed, to the “amplitude saturation” regime, where the rms interface elevation is independent of the gas flow rate. While some wave breaking events are observed also in the wave-growth regime, wave breaking is found to be much more frequent when the gas flow rate is increased into the amplitude saturation regime, and 35%-40% of the waves passing the measurement section are assessed to be in a state of active breaking in this regime. A conditional averaging of the flow field is performed, and the turbulent dissipation rate below breaking and non-breaking waves is estimated. The effect of microscale breaking is observed down to a depth of 10 mm below the water surface. Below the crest of microscale breaking waves, the turbulent dissipation rate is increased by a factor 2.5 to 4 compared with non-breaking waves. This fraction increases with Usg, implying that the breaking events become more energetic as the gas flow rate is increased.

Influence Factors of Fracture Mechanics Analysis of Reactor Pressure Vessel under Pressurized Thermal Shock

When the reactor pressure vessel (RPV) is subjected to pressurized thermal shock (PTS), the cooling water injected by the emergency core cooling system (ECCS) will generate a large temperature difference in the wall thickness of the pressure vessel. On the other hand, the fracture toughness of the RPV material decreases a lot under long-term neutron irradiation. Under this condition, the PTS transient may cause a rapid growth of defects in the inner surface of the vessel, resulting in failure of the pressure vessel. In this paper, the fracture mechanics analysis method of RPV under pressurized thermal shock is studied. The thermal analysis and structural analysis of the pressure vessel are performed by finite element method. The stress intensity factor and fracture toughness are obtained through calculation. At the same time, the influence factors of fracture mechanics analysis of RPV under PTS condition are analyzed. The effects of different crack size, crack type, load transient, and neutron irradiation flux on the PTS fracture mechanics analysis results are evaluated. Results show that the larger the ratio of length to depth for axial inner surface cracks, the easier RPV crack grows. Under small break condition, the circumferential cracks are safer than axial cracks. The longer the operating time, the more severe the embrittlement of RPV materials, which will lead to the failure of RPV more easily. For the two typical PTS transients studied in this paper, the re-pressurization condition is safer than the small break condition. The results can provide basis for structural integrity assessment of RPV under PTS condition.

Probing color reconnection with underlying event observables at the LHC energies

In this work, we study the underlying-event (UE) activity as a function of the highest jet or charged-particle transverse momentum (${p}_{\mathrm{T}}^{\text{jet}}$ or ${p}_{\mathrm{T}}^{\text{leading}}$) in terms of number and summed-${p}_{\mathrm{T}}$ densities of charged particles in the azimuthal region transverse to the leading jet or particle direction. Contrary to inelastic $pp$ LHC data, the UE observables normalized to the charged-particle density obey an approximate Koba-Nielsen-Olesen (KNO) scaling. Based on PYTHIA 8.2 simulations of $pp$ collisions at LHC energies, we show that the small breaking of the KNO scaling is due to the increasing importance of multiple partonic interactions (MPI) at higher $\sqrt{s}$. This in turn makes that with increasing energy, the ${p}_{\mathrm{T}}$ spectra in the UE get harder than in inelastic $pp$ collisions. Color reconnection (CR) models the interactions among outgoing partons just before the hadronization; therefore, it modifies the ${p}_{\mathrm{T}}$-spectral shape. Motivated by this, we studied the UE activity considering charged particles within different ${p}_{\mathrm{T}}$ intervals in $pp$ collisions at $\sqrt{s}=7\text{ }\text{ }\mathrm{TeV}$. Although MPI saturate for ${p}_{\mathrm{T}}^{\text{jet}}>10\text{ }\text{ }\mathrm{GeV}/c$, the UE still increases with increasing ${p}_{\mathrm{T}}^{\text{jet}}$. We demonstrate that the saturation of both number and summed-${p}_{\mathrm{T}}$ densities, which are commonly claimed, are only observed for low-${p}_{\mathrm{T}}$ charged particles ($0.5<{p}_{\mathrm{T}}<2\text{ }\text{ }\mathrm{GeV}/c$). Moreover, for the ${p}_{\mathrm{T}}$-integrated case (${p}_{\mathrm{T}}>0.5\text{ }\text{ }\mathrm{GeV}/c$), the summed-${p}_{\mathrm{T}}$ density is not sensitive to the variation of CR; however, at low-${p}_{\mathrm{T}}$, it is reduced with increasing CR, whereas an opposite behavior is found at intermediate ${p}_{\mathrm{T}}$ ($2<{p}_{\mathrm{T}}<10\text{ }\text{ }\mathrm{GeV}/c$). Finally, we show that CR produces flowlike behavior only in the UE region, and the effects are reduced with increasing ${p}_{\mathrm{T}}^{\text{jet}}$ due to the hardening of UE. The outcomes encourage the measurement of inclusive and identified charged-particle ${p}_{\mathrm{T}}$ spectra (over a wide range of ${p}_{\mathrm{T}}$) associated to UE aimed at better understanding the similarities between $pp$ and heavy-ion data discovered at the LHC.

Variability of plant risk due to variable operator allowable time for aggressive cooldown initiation

Abstract Recent analysis results with realistic assumptions provide the variability of operator allowable time for the initiation of aggressive cooldown under small break loss of coolant accident or steam generator tube rupture with total failure of high pressure safety injection. We investigated how plant risk may vary depending on the variability of operators’ failure probability of timely initiation of aggressive cooldown. Using a probabilistic safety assessment model of a nuclear power plant, we showed that plant risks had a linear relation with the failure probability of aggressive cooldown and could be reduced by up to 10% as aggressive cooldown is more reliably performed. For individual accident management, we found that core damage potential could be gradually reduced by up to 40.49% and 63.84% after a small break loss of coolant accident or a steam generator tube rupture, respectively. Based on the importance of timely initiation of aggressive cooldown by main control room operators within the success criteria, implications for improvement of emergency operating procedures are discussed. We recommend conducting further detailed analyses of aggressive cooldown, commensurate with its importance in reducing risks in nuclear power plants.

Scaling and integral effect test on transition from depressurization to long-term gravity injection

The passive safety commercial pressurized water reactors (PWRs), AP1000 and CAP1400 are equipped with the automatic depressurization system (ADS). The fourth stage of ADS (ADS-4) has the largest discharging capacity among the all ADS stages. During a small break loss-of-coolant accident (SBLOCA), only when the system is fully depressurized by the ADS-4 to near the containment atmospheric pressure, the in-containment refueling water storage tank (IRWST) can deliver the large coolant inventory for the long-term core cooling by its water head. Before the IRWST injection, the core reaches its minimum inventory. So the transition from the ADS-4 depressurization to the IRWST injection is a very challenging period in a SBLOCA. Therefore, to evaluate the passive system performance by the integral effect test (IET), the transition must be simulated properly. This work conducted the scaling analysis for the ADS-4 depressurization and the IRWST injection for designing the related components of the ACME IET facility. A uniform scaling law based on the existing T-branch liquid entrainment models was proposed. For scaling the onset of the IRWST injection, the requirement for reproducing the synergetic effect in an IET was introduced in order to preserve the important event/process occurrence time with the proper conditions, and the scaling laws for the full pressure IRWST injection were obtained. For investigating the transition thermal hydraulic behaviors and the ADS-4 configuration influences on the core safety, one cold leg break test and three double-ended direct-vessel-injection (DEDVI) line break tests with the different ADS-4 failure modes were selected from the ACME SBLOCA test matrix, and the main test data related to the core safety were analyzed and compared. It was found that the ADS-4 actuation significantly accelerated the system depressurization but worsened the core inventory depletion at the same time. In addition, the break condition and the ADS-4 failure mode could differently affect the system depressurization and the core level. The ACC injection during the ADS-4 depressurization in DEDVI was critical for the core level makeup. The insufficient ADS-4 venting capacity delayed IRWST injection, but also mitigated the core inventory depletion. It suggests the ADS-4 design can be potentially optimized in the passive safety system design.

Fluoropyrimidine-induced intestinal mucosal injury is associated with the severity of chemotherapy-related diarrhea

Background and aim: Although the fluoropyrimidines are effective chemotherapeutic agents for malignant gastrointestinal tumors, they sometimes cause enteritis with diarrhea. Severe treatment-related diarrhea may result in chemotherapy discontinuation. We investigated the relationship between diarrhea severity and fluoropyrimidine-induced small intestinal mucosal injury.Methods: We performed small bowel capsule endoscopy in patients undergoing chemotherapy including fluoropyrimidine for a malignant tumor between May 2017 and June 2018 and analyzed the relationship between the endoscopic findings and diarrhea severity. We also performed a cross-sectional analysis of patient factors and routes of chemotherapy to identify risk factors of fluoropyrimidine-induced small intestinal injury.Results: Small bowel capsule endoscopy was successfully completed in 16 eligible patients. The diarrhea grade (per the Common Terminology Criteria for Adverse Events, version 4.0) was significantly correlated with the percentage of patients with a small intestinal mucosal break (grade 0, 16.7%; grade 1, 57.1%; grade 2, 100%; p = .016, Cochran-Armitage trend test). Compared to patients receiving intravenous therapy, those receiving an orally administered fluoropyrimidine had a significantly greater number of small intestinal mucosal breaks (median number of breaks [range]; intravenous 5-fluorouracil, 0 [0–13]; oral fluoropyrimidine, 6.5 [1–20]; p = .0162, Mann–Whitney U test).Conclusions: Many patients with diarrhea caused by chemotherapy including fluoropyrimidine had small intestinal mucosal breaks. Additionally, small intestinal mucosal breaks were more severe in patients receiving a regimen of oral treatment than in those receiving a regimen of intravenous therapy. These outcomes have important implications for investigations of new strategies for preventing anti-cancer drug-induced diarrhea.

A study on a minimally broken residual TBM-Klein symmetry with its implications on flavoured leptogenesis and ultra high energy neutrino flux ratios

We present a systematic study on minimally perturbed neutrino mass matrices which at the leading order give rise to Tri-BiMaximal (TBM) mixing due to a residual ℤ2× ℤ2μτ Klein symmetry in the neutrino mass term of the low energy effective seesaw Lagrangian. Considering only the breaking of ℤ2μτ with two relevant breaking parameters (ϵ4,6′), after a comprehensive numerical analysis, we show that the phenomenologically viable case in this scenario is a special case of TM1 mixing. For this class of models, from the phenomenological perspective, one always needs large breaking (more than 45%) in one of the breaking parameters. However, to be consistent the maximal mixing of θ23, while more than 35% breaking is needed in the other, a range 49.4̂−53̂ and 38̂−40̂ could be probed allowing breaking up to 25% in the same parameter. Thus though this model cannot distinguish the octant of θ23, non-maximal mixing is preferred from the viewpoint of small breaking. The full ℤ2× ℤ2μτ symmetry leads to a degeneracy in the eigenvalues of right handed (RH) neutrino mass matrices (MR). Nevertheless, breaking of ℤ2μτ which is also necessary to generate nonzero θ13 in this model, lifts that degeneracy. Thus unlike the standard N1-leptogenesis scenario where only the decays and other interactions due to the lightest RH neutrino N1 are relevant, here all the RH neutrinos contribute to the process of baryogenesis via leptogenesis due to the small mass splitting controlled by the ℤ2μτ breaking parameters. Including flavour coupling effects (In general, which have been partially included in all the leptogenesis studies in perturbed TBM framework), we solve flavour dependent coupled Boltzmann equations for heavy neutrino as well as the light leptonic number densities to compute the final baryon asymmetry YB. Thus our analysis and results pertaining to a successful leptogenesis are more accurate than any other studies in existing literature that deal with perturbed TBM scenario. Finally, in the context of recent discovery of the ultra high energy (UHE) neutrino events at IceCube, assuming UHE neutrinos originate from purely astrophysical sources, we obtain prediction on the neutrino flux ratios at neutrino telescopes.

Denying, downplaying, debating: defensive discourses of inequality in the debate on Piketty

ABSTRACTA clear sign of the heightened interest in economic inequality was the surprise popularity of Thomas Piketty’s Capital in the twenty-first century. The book reached the top of the bestseller lists and was described as a ‘media sensation’ and Piketty himself as a ‘rockstar economist’. Piketty’s key thesis stated that the return on investment will be higher than economic growth (r > g), meaning that inequality is destined to worsen and that the post-war Keynesian period of progress, in terms of a flattening of inequality, was in fact a small break from the norm. What he termed patrimonial capitalism would see continual increases in rates of socio-economic inequality unless drastic action is taken. In this article, Piketty’s book is treated as a paramount example of the mediation of economic inequality. The book received a generally positive response, however some writers acted defensively against the book’s main thesis, that is the secular trend of growing inequality. Exploring the press in the UK, Germany, Ireland and Austria we investigate what we term defensive discourses on inequality, meaning discourses which act to downplay, deny or conflate Piketty’s findings including discourses challenging his data and methods, discourses defending inequality as a necessity and discourses opposing regulation.

An international and interdisciplinary approach on learning how to design a space station

The Space Station Design Workshop (SSDW), instigated by the Institute of Space Systems (IRS) at the University of Stuttgart, is an international and interdisciplinary workshop, targeted to undergraduate and graduate students as well as young professionals. The first workshop started in 1996, and except for some small breaks, it has taken place on a yearly basis. Currently, 40 participants are divided into two teams, which within six days have to fulfil one goal: to design a space station. The goal of the workshop is to obtain creative solutions from young and fresh minds, but also to enable students to learn by doing how an interdisciplinary and international project works. Several tools are provided by the IRS for the entire week: internal/external experts on the required fields; a concurrent design facility and specialized software. As the conceptual design needs to be created in a short period of time, the entire process is monitored by the IRS staff. This guidance should however not compromise the creativity and the “out-the box thinking” of the participants. The experience of previous editions and the lessons learned help improving this guidance process year after year. This paper explains the teaching approach using the activities during the SSDW 2017 as an example, starting from the mission statement to the final presentation. As a conclusion, the evaluation and opinions of the experts, the students and the organization staff are presented, as well as the main lessons learned, including how they can be implemented to further improve the SSDW.

Actividad física y fibromialgia. Un acercamiento a la intención de caminar a través del estudio de las creencias

Introducción: La fibromialgia es un trastorno crónico que cursa con dolor músculo-esquelético generalizado, con frecuencia acompañado de numerosa comorbilidad. Dentro de la necesidad de un abordaje multidisciplinar, el ejercicio físico aeróbico se recomienda como tratamiento de primera elección. Objetivo: Analizar las creencias, bajo el modelo de la Teoría de la Acción Planeada, asociadas a la intención de “caminar 2-4 veces por semana, un mínimo de 30 minutos, intercalando un pequeño descanso, durante al menos 6 semanas consecutivas”. Método: se utilizó un diseño longitudinal con dos medidas (T1-T2) con una diferencia de 6 semanas, con 275 (T1) y 219 (T2) mujeres con fibromialgia. Resultados: Existe una tendencia a la significación en la relación entre intención y conducta de caminar (x2= 3.336, p=.068). Se observan diferencias estadísticamente significativas en las creencias comportamentales positivas (p=.004), en las creencias comportamentales negativas (p=.008) y en las creencias normativas prescriptivas (p=.002) entre las pacientes con alta y baja intención.La recomendación medica de caminar y la intensidad de dolor percibida se asocian significativamente con las creencias comportamentales positivas y con las creencias de control inhibidoras. Conclusiones: La intención de caminar según la pauta establecida se relaciona con creencias comportamentales positivas relativas a consecuencias generales de salud, y no a la mejora específica de la sintomatología relacionada con la fibromialgia.

Simulation of SB-LOCA of typical PWR with MELCOR code

Safety of Nuclear Power Plants (NPPs) is one of the main issues in nuclear industry mainly because of the probability of radionuclides release to the environment. Due to this fact nuclear safety is continuously being improved by vendors to face the growing demands especially after the accident in Fukushima. This accident because of its character (station blackout scenario) resulted in putting more emphasis than ever on passive safety systems in NPPs. Such systems are one of main focus points in presented simulation. One of the ways to improve NPPs’ safety and check its robustness is to proceed simulations of different events and find the weakest points inside the system. First thing is to create simulation model of NPP which has to be validated in order to prove reliability of future results. This paper presents simulation run of design basis accident for large PWR reactor based on AP1000. Model was developed using publicly available data only, which means that it should be considered only as “AP1000-like model”. MELCOR code which was used in presented calculations is a severe accident code which simulates core melting during the worst possible accidents in NPP. Here it was decided to simulate design basis accident namely small break loss of coolant accident (SB-LOCA) and compare obtained results with those from the safety reports. Main motivation to create such simulation was to increase authors’ knowledge about MELCOR behaviour and sensitivity in case of thermal hydraulic response to learn what kind of errors and uncertainty could be expect. Second motivation was to check if Melcor is capable to simulate design basis accident with acceptable results. Finally the obtained results are in relatively good agreement with the expectations and some differences that have appeared do not affect general course of the accident. Shape of transient curves and timing of events are reasonable correct.

Best-estimate calculation plus uncertainty analysis of SBLOCA transient for the scale-down passive test facility

CAP1400 has been developed as a new passive nuclear power plant in China based on AP1000 technique. In order to support the CAP1400 licensing, a scale-down integral test facility named ACME (Advanced Core-cooling Mechanism Experiment) has been designed and constructed. In this study, best-estimate calculation using RELAP5/MOD3.4 code plus uncertainty quantification and sensitivity analysis of the small break loss of coolant accident (SBLOCA) transient were carried out for the ACME test facility. The important thermal-hydraulic phenomena during the SBLOCA transient were investigated through the comparing calculations between the ACME and CAP1400. Thereafter, uncertainty quantification process was demonstrated including the selection of input uncertain parameters, the application of Wilks’ nonparametric statistics and the propagation of uncertainty through the SNAP interface coupling RELAP5 and DAKOTA codes. Furthermore, the results of uncertainty and sensitivity analysis were discussed. Through the comparison of the thermal-hydraulic modeling results between ACME and CAP1400, the results show that the ACME test facility is able to reproduce the important thermal-hydraulic phenomena of CAP1400 by reasonable scaling design. The 95/95 uncertainty bands of some key output parameters are obtained through uncertainty quantification. The lower band of the minimum core level is maintained still above the top of the active core section, thus the core uncover will not occur with 95% confidence level. Important input uncertain contributors for the minimum core level are identified through the measure of Spearman rank correlation coefficients in sensitivity analysis. The demonstration of best-estimate plus uncertainty analysis (BEPU) application will provide some guidance for the safety analysis of advanced passive nuclear power plants.

SO(4) invariant Higgs-Yukawa model with reduced staggered fermions

We explore the phase structure of a four dimensional $SO(4)$ invariant lattice Higgs-Yukawa model comprising four reduced staggered fermions interacting with a real scalar field. The fermions belong to the fundamental representation of the symmetry group while the three scalar field components transform in the self-dual representation of $SO(4)$. The model is a generalization of a four fermion system with the same symmetries that has received recent attention because of its unusual phase structure comprising massless and massive symmetric phases separated by a very narrow phase in which a small bilinear condensate breaking $SO(4)$ symmetry is present. The generalization described in this paper simply consists of the addition of a scalar kinetic term. We find a region of the enlarged phase diagram which shows no sign of a fermion condensate or symmetry breaking but in which there is nevertheless evidence of a diverging correlation length. Our results in this region are consistent with the presence of a single continuous phase transition separating the massless and massive symmetric phases observed in the earlier work.

Anachronistic facies and carbon isotopes during the end-Permian biocrisis: Evidence from the mid-Tethys (Kisejin, Iran)

Late Permian mass extinction (LPME) research has focused primarily on Tethyan sections because it is believed that these successions are more complete than those from other localities, and provide a more comprehensive record of the largest, most devastating extinction event in Earth history. The Kisejin section, a previously undocumented mid-Tethyan, Upper Permian-Lower Triassic succession located in the Central-Iran Plate. The Kisejin section contains a continuous Permian-Triassic sequence with only small breaks in sedimentation and was examined in order to determine sedimentologic, biostratigraphic, and carbon isotopic trends across the Permian-Triassic transition. Abnormal (anachronistic) carbonates developed in the study area following the LPME, and include microbialites, edgewise conglomerates, sparitic microspheres, and microbially-coated grains; microbialites occur as thrombolites, stromatolites, and as agglutinated forms. Renalcis-type calcimicrobes are documented for the first time from Permian-Triassic boundary microbialites (PTBMs) of Iran. Coated grains fall into two groups, and include pre-PTBM ooids, which are dense and cloudy, and possibly microbial in origin, and post-PTBM cortoids with destructive and constructive micrite envelopes. Latest Permian conodonts (H. praeparvus, M. ultima), coupled with carbon isotopic values, place the Permian-Triassic boundary within the lowermost thrombolite unit, about 2.1 m above the boundary between the Nessen Formation and the Elika Formation, and indicate that microbialite growth began during the latest Permian. Our study of this previously unknown section shows that, unlike other well-known PTB sections from Iran, the microbialite pattern is complicated, and is more similar to PTBM successions from Turkey. In addition, we note a similarity between the unusual facies of the Kisejin section and those of eastern Tethyan sections from China (i.e. sparry microspheres and Renalcis-type calcimicrobes); these unusual facies have not been previously reported from other well-known Iranian sections, including Julfa and Abadeh, which are thick and have been extensively studied.

Pilot Study Indicates Helicobacter pylori Infection May Induce Small Intestinal Mucosal Injury

Background and Aim: Helicobacter pylori infection is a primary cause of gastroduodenal ulcers. To investigate whether there is an association between H. pylori infection and small intestinal mucosal injury. Methods: Patients were selected from a general pool of subjects who underwent capsule endoscopy for current or past obscure gastrointestinal bleeding. Characteristics including age, gender, history, treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) and/or acid suppressant, diagnosis, and H. pylori infection were investigated. Patients infected with H. pylori had positive test result, ranging 30 days before to 30 days after capsule endoscopy. Patients diagnosed with inflammatory diseases, malignant tumors, etc. were excluded. All video images were re-evaluated to count small intestinal mucosal breaks. Eligible patient variables were compared. Results: A total of 92 patients (30 infected with H. pylori/62 uninfected) were eligible. By univariate analysis of the number of mucosal breaks, patients treated with NSAIDs were found to have more mucosal breaks than patients untreated (38%: 8/21 vs. 18%: 13/71; p = 0.004), and the possible association was detected between patients infected with H. pylori and those who were not (67%: 14/21 vs. 37%: 26/71; p = 0.081). When comparing the H. pylori infected and uninfected patients, the rate of patients with mucosal breaks was greater in infected patients (47%: 14/30 vs. 11%: 7/62; p = 0.001). After excluding patients treated with NSAIDs, the number of mucosal breaks was also greater in patients infected with H. pylori (1.2 ± 1.5 vs. 0.38 ± 0.62; p = 0.001). Conclusion: There is a possibility that H. pylori infection induces small intestinal mucosal injury.

Fatigue crack initiation and subsequent crack growth in fillet welded steel joints

The fatigue damage evolution in fillet welded steel joints where cracks are emanating from the weld toe is investigated. Based on existing experimental data for as-welded joints including crack depth measurements of the early crack growth it is proposed to make a distinction between the crack initiation phase and the subsequent crack growth phase. The welded detail in question is an F class detail with plate thickness 25 mm made of medium strength carbon steel. It is found that the crack initiation phase defined at a crack depth of 0.1 mm is close to 25% of the fatigue life even at a relatively high constant stress range of 150 MPa. At lower stress ranges it is concluded that the initiation phase is the dominating part of the fatigue life. The present work is focusing on the crack propagation phase that is defined from a crack depth of 0.1 mm to final failure of the detail. It is demonstrated that the recommendation given in rules and recommendations (DNVGL and BS 7910) for applying Linear Elastic Fracture Mechanics (LEFM) for the crack propagation phase is valid for the propagation of such small surface breaking cracks. A model based on the rule-based formulas for the Stress Intensity Factor Range (SIFR) and the growth parameters C and m in Paris law agree well the with the measured crack growth curves. For these small semi-elliptical cracks at the weld toe notch important topics like the existence of a threshold limit for the SIFR and the influence of the stress ratio R are discussed. Due to the inherent scatter in the variables characterizing the fatigue damage evolution stochastic approaches are applied for the analyses. Observations and measurements are presented by descriptive statistics and simulations are carried out using Monte Carlo techniques.