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1.
Phys Rev E ; 104(4-1): 044311, 2021 Oct.
Article in English | MEDLINE | ID: mdl-34781443

ABSTRACT

We consider a dynamic network of individuals that may hold one of two different opinions in a two-party society. As a dynamical model, agents can endlessly create and delete links to satisfy a preferred degree, and the network is shaped by homophily, a form of social interaction. Characterized by the parameter J∈[-1,1], the latter plays a role similar to Ising spins: agents create links to others of the same opinion with probability (1+J)/2 and delete them with probability (1-J)/2. Using Monte Carlo simulations and mean-field theory, we focus on the network structure in the steady state. We study the effects of J on degree distributions and the fraction of cross-party links. While the extreme cases of homophily or heterophily (J=±1) are easily understood to result in complete polarization or anti-polarization, intermediate values of J lead to interesting features of the network. Our model exhibits the intriguing feature of an "overwhelming transition" occurring when communities of different sizes are subject to sufficient heterophily: agents of the minority group are oversubscribed and their average degree greatly exceeds that of the majority group. In addition, we introduce an original measure of polarization which displays distinct advantages over the commonly used average edge homogeneity.

2.
Phys Rev E ; 104(6-1): 064135, 2021 Dec.
Article in English | MEDLINE | ID: mdl-35030961

ABSTRACT

An investigation of the two-dimensional Widom-Rowlinson lattice gas under an applied drive uncovered a remarkable nonequilibrium steady state in which uniform stripes (reminiscent of an equilibrium lamellar phase) form perpendicular to the drive direction [R. Dickman and R. K. P. Zia, Phys. Rev. E 97, 062126 (2018)10.1103/PhysRevE.97.062126]. Here we study this model at low particle densities in two and three dimensions, where we find a disordered phase with a characteristic length scale (a "microemulsion") along the drive direction. We develop a continuum theory of this disordered phase to derive a coarse-grained field-theoretic action for the nonequilibrium dynamics. The action has the form of two coupled driven diffusive systems with different characteristic velocities, generated by an interplay between the particle repulsion and the drive. We then show how fluctuation corrections in the field theory may generate the characteristic features of the microemulsion phase, including a peak in the static structure factor corresponding to the characteristic length scale. This work lays the foundation for understanding the stripe phenomenon more generally.

3.
Phys Rev E ; 99(2-1): 022309, 2019 Feb.
Article in English | MEDLINE | ID: mdl-30934283

ABSTRACT

When three species compete cyclically in a well-mixed, stochastic system of N individuals, extinction is known to typically occur at times scaling as the system size N. This happens, for example, in rock-paper-scissors games or conserved Lotka-Volterra models in which every pair of individuals can interact on a complete graph. Here we show that if the competing individuals also have a "social temperament" to be either introverted or extroverted, leading them to cut or add links, respectively, then long-living states in which all species coexist can occur. These nonequilibrium quasisteady states only occur when both introverts and extroverts are present, thus showing that diversity can lead to stability in complex systems. In this case, it enables a subtle balance between species competition and network dynamics to be maintained.

4.
Phys Rev E ; 97(6-1): 062126, 2018 Jun.
Article in English | MEDLINE | ID: mdl-30011593

ABSTRACT

In the Widom-Rowlinson lattice gas, two particle species (A, B) diffuse freely via particle-hole exchange, subject to both on-site exclusion and prohibition of A-B nearest-neighbor pairs. As an athermal system, the overall densities are the only control parameters. As the densities increase, an entropically driven phase transition occurs, leading to ordered states with A- and B-rich domains separated by hole-rich interfaces. Using Monte Carlo simulations, we analyze the effect of imposing a drive on this system, biasing particle moves along one direction. Our study parallels that for a driven Ising lattice gas, the Katz-Lebowitz-Spohn (KLS) model, which displays atypical collective behavior, e.g., structure factors with discontinuity singularities and ordered states with domains only parallel to the drive. Here, other interesting features emerge, including structure factors with kink singularities (best fitted to |q|), maxima at nonvanishing wave-vector values, oscillating correlation functions, and ordering into multiple striped domains perpendicular to the drive, with a preferred wavelength depending on density and drive intensity. Moreover, the (hole-rich) interfaces between the domains are statistically rough (whether driven or not), in sharp contrast with those in the KLS model, in which the drive suppresses interfacial roughness. Defining an order parameter that accounts for the emergence of multistripe states, we map out the phase diagram in the density-drive plane and present preliminary evidence for a critical phase in this driven lattice gas.

5.
Anim Reprod Sci ; 187: 181-192, 2017 Dec.
Article in English | MEDLINE | ID: mdl-29126830

ABSTRACT

The normal maturation and ovulation from ovarian follicles is important in ensuring conception and improving fertility of buffalo. The molecular regulation mechanism of buffalo follicles growth, however, remains unknown. This study analyzed the gene expression profiles associated with buffalo ovarian follicle growth. According to the analysis of RNA sequencing, 17,700 unigenes and 13,672 differentially expressed genes (DEGs) were detected. A total of 30 common DEGs were identified during four stages of follicle growth, and the expression patterns are basically synchronized, suggesting the products as a result of expressions of these genes may cooperate to regulate follicular development. Furthermore, GO and KEGG enrichment analyses revealed that the majority of DEGs in early stage of follicular growth were enriched in ribosomal and oxidative phosphorylation signaling pathways, and the expression patterns of these DEGs are basically up-regulated at the beginning of follicular growth (<8mm, diameter), and then down-regulated (8-12mm) in the following stages of follicular development. The pathway of immune signaling, including allograft rejection, chemokine signaling pathway, natural killer cell mediated cytotoxicity, phagosome, and antigen processing and presentation, was significantly enriched in the last stage of follicular development (>12mm), which indicates that the immune system has an important role in the last stage of follicular maturation and ovulation. This study provided a gene expression profile of buffalo follicle growth, and provided an insight into biological processes associated with molecular regulation of ovarian follicle growth.


Subject(s)
Buffaloes/genetics , Gene Expression Regulation, Developmental , Granulosa Cells/metabolism , Ovarian Follicle/metabolism , Ovulation/metabolism , Transcriptome , Animals , Buffaloes/growth & development , Female , Gene Expression Profiling/methods , Granulosa Cells/cytology , Ovarian Follicle/cytology , Ovulation/genetics , Sequence Analysis, RNA/methods , Signal Transduction
6.
Phys Rev E ; 95(1-1): 012104, 2017 Jan.
Article in English | MEDLINE | ID: mdl-28208330

ABSTRACT

We study the dynamics of the out-of-equilibrium nonlinear q-voter model with two types of susceptible voters and zealots, introduced in Mellor et al. [Europhys. Lett. 113, 48001 (2016)EULEEJ0295-507510.1209/0295-5075/113/48001]. In this model, each individual supports one of two parties and is either a susceptible voter of type q_{1} or q_{2}, or is an inflexible zealot. At each time step, a q_{i}-susceptible voter (i=1,2) consults a group of q_{i} neighbors and adopts their opinion if all group members agree, while zealots are inflexible and never change their opinion. This model violates detailed balance whenever q_{1}≠q_{2} and is characterized by two distinct regimes of low and high density of zealotry. Here, by combining analytical and numerical methods, we investigate the nonequilibrium stationary state of the system in terms of its probability distribution, nonvanishing currents, and unequal-time two-point correlation functions. We also study the switching time properties of the model by exploiting an approximate mapping onto the model of Mobilia [Phys. Rev. E 92, 012803 (2015)PLEEE81539-375510.1103/PhysRevE.92.012803] that satisfies the detailed balance, and we outline some properties of the model near criticality.

7.
Article in English | MEDLINE | ID: mdl-25974435

ABSTRACT

In common descriptions of phase transitions, first-order transitions are characterized by discontinuous jumps in the order parameter and normal fluctuations, while second-order transitions are associated with no jumps and anomalous fluctuations. Outside this paradigm are systems exhibiting "mixed-order" transitions displaying a mixture of these characteristics. When the jump is maximal and the fluctuations range over the entire range of allowed values, the behavior has been coined an "extreme Thouless effect." Here we report findings of such a phenomenon in the context of dynamic, social networks. Defined by minimal rules of evolution, it describes a population of extreme introverts and extroverts, who prefer to have contacts with, respectively, no one or everyone. From the dynamics, we derive an exact distribution of microstates in the stationary state. With only two control parameters, N(I,E) (the number of each subgroup), we study collective variables of interest, e.g., X, the total number of I-E links, and the degree distributions. Using simulations and mean-field theory, we provide evidence that this system displays an extreme Thouless effect. Specifically, the fraction X/(N(I)N(E)) jumps from 0 to 1 (in the thermodynamic limit) when N(I) crosses N(E), while all values appear with equal probability at N(I)=N(E).

8.
Hawaii J Med Public Health ; 74(1): 16-20, 2015 Jan.
Article in English | MEDLINE | ID: mdl-25628978

ABSTRACT

Recent efforts directed at potential litigation in Hawai'i have resulted in a renewed interest for genetic screening for cytochrome P450 2C19 (CYP2C19) polymorphisms in patients treated with clopidogrel. Clopidogrel is an antiplatelet agent, frequently used in combination with aspirin, for the prevention of thrombotic complications with acute coronary syndrome and in patients undergoing percutaneous coronary interventions. Cytochrome P-450 (CYP) 2C19 is an enzyme involved in the bioactivation of clopidogrel from a pro-drug to an active inhibitor of platelet action. Patients of Asian and Pacific Island background have been reported to have an increase in CYP2C19 polymorphisms associated with loss-of-function of this enzyme when compared to other ethnicities. This has created an interest in genetic testing for CYP2C19 polymorphisms in Hawai'i. Based upon our review of the current literature, we do not feel that there is support for the routine screening for CYP2C19 polymorphisms in patients being treated with clopidogrel; furthermore, the results of genetic testing may not be helpful in guiding therapeutic decisions. We recommend that decisions on the type of antiplatelet treatment be made based upon clinical evidence of potential differential outcomes associated with the use of these agents rather than on the basis of genetic testing.


Subject(s)
Cytochrome P-450 CYP2C19/genetics , Genetic Testing/methods , Ticlopidine/analogs & derivatives , Clopidogrel , Hawaii , Humans , Mass Screening , Polymorphism, Genetic , Ticlopidine/adverse effects , Ticlopidine/therapeutic use
9.
Article in English | MEDLINE | ID: mdl-25314395

ABSTRACT

Motivated by fundamental issues in nonequilibrium statistical mechanics, we study the venerable susceptible-infected-susceptible (SIS) model of disease spreading in an idealized, simple setting. Using Monte Carlo and analytic techniques, we consider a fully connected, unidirectional network of odd number of nodes, each having an equal number of in- and out-degrees. With the standard SIS dynamics at high infection rates, this system settles into an active nonequilibrium steady state. We find the exact probability distribution and explore its implications for nonequilibrium statistical mechanics, such as the presence of persistent probability currents.


Subject(s)
Epidemics , Models, Statistical , Monte Carlo Method , Communicable Diseases/epidemiology , Communicable Diseases/transmission , Disease Susceptibility , Probability
10.
Article in English | MEDLINE | ID: mdl-25615050

ABSTRACT

The statistical mechanics of a one-dimensional Ising model in thermal equilibrium is well-established, textbook material. Yet, when driven far from equilibrium by coupling two sectors to two baths at different temperatures, it exhibits remarkable phenomena, including an unexpected "freezing by heating." These phenomena are explored through systematic numerical simulations. Our study reveals complicated relaxation processes as well as a crossover between two very different steady-state regimes.

11.
Article in English | MEDLINE | ID: mdl-23496498

ABSTRACT

In an accelerated exclusion process (AEP), each particle can "hop" to its adjacent site if empty as well as "kick" the frontmost particle when joining a cluster of size ℓ≤ℓ(max). With various choices of the interaction range, ℓ(max), we find that the steady state of AEP can be found in a homogeneous phase with augmented currents (AC) or a segregated phase with holes moving at unit velocity (UV). Here we present a detailed study on the emergence of the novel phases, from two perspectives: the AEP and a mass transport process (MTP). In the latter picture, the system in the UV phase is composed of a condensate in coexistence with a fluid, while the transition from AC to UV can be regarded as condensation. Using Monte Carlo simulations, exact results for special cases, and analytic methods in a mean field approach (within the MTP), we focus on steady state currents and cluster sizes. Excellent agreement between data and theory is found, providing an insightful picture for understanding this model system.


Subject(s)
Diffusion , Models, Chemical , Models, Statistical , Quantum Theory , Solutions/chemistry , Computer Simulation , Monte Carlo Method
12.
PLoS One ; 7(11): e48686, 2012.
Article in English | MEDLINE | ID: mdl-23189133

ABSTRACT

We study the standard SIS model of epidemic spreading on networks where individuals have a fluctuating number of connections around a preferred degree κ. Using very simple rules for forming such preferred degree networks, we find some unusual statistical properties not found in familiar Erdös-Rényi or scale free networks. By letting κ depend on the fraction of infected individuals, we model the behavioral changes in response to how the extent of the epidemic is perceived. In our models, the behavioral adaptations can be either 'blind' or 'selective'--depending on whether a node adapts by cutting or adding links to randomly chosen partners or selectively, based on the state of the partner. For a frozen preferred network, we find that the infection threshold follows the heterogeneous mean field result λ(c)/µ = <κ>/<κ2> and the phase diagram matches the predictions of the annealed adjacency matrix (AAM) approach. With 'blind' adaptations, although the epidemic threshold remains unchanged, the infection level is substantially affected, depending on the details of the adaptation. The 'selective' adaptive SIS models are most interesting. Both the threshold and the level of infection changes, controlled not only by how the adaptations are implemented but also how often the nodes cut/add links (compared to the time scales of the epidemic spreading). A simple mean field theory is presented for the selective adaptations which capture the qualitative and some of the quantitative features of the infection phase diagram.


Subject(s)
Epidemics/statistics & numerical data , Models, Theoretical , Algorithms , Computer Simulation , Humans
13.
Aust Dent J ; 57(3): 355-8, 2012 Sep.
Article in English | MEDLINE | ID: mdl-22924361

ABSTRACT

BACKGROUND: The aim of this study was to reveal the incidence and distribution pattern of craniofacial pain of cardiac origin. METHODS: We undertook a prospective study of 248 consecutive patients (aged 26 to 88 years) hospitalized with confirmed cardiac ischaemic periods. Digital OPG radiographs were obtained from all patients for radiographic examination of the jaws and dentition. Patients underwent clinical and radiographic examinations, and symptoms were evaluated in detail to determine the prevalence and distribution pattern of craniofacial pain of cardiac origin. RESULTS: Craniofacial pain was the sole symptom of cardiac ischaemia in 13 patients (5.2%); two developed acute myocardial infarction (AMI). Pain in the craniofacial region, chest, shoulders and arms was experienced by 72 patients. The most frequently affected region was the left mandible. In the absence of chest pain, patients most frequently experienced pain in craniofacial structures. Incidence of craniofacial pain was significantly higher in females than males (p = 0.024). CONCLUSIONS: Cardiac pain commonly radiates to the craniofacial structures. Pain of cardiac origin is usually described as pressure and/or a burning sensation that is provoked by physical activity and relieved by rest. Craniofacial pain of cardiac origin usually occurs bilaterally. Dental practitioners can play a crucial role in the diagnosis of craniofacial pain of cardiac origin.


Subject(s)
Facial Pain/etiology , Myocardial Ischemia/complications , Adult , Aged , Aged, 80 and over , Female , Humans , Incidence , Male , Middle Aged , Myocardial Ischemia/diagnosis , Prospective Studies , Radiography, Dental, Digital , Sex Distribution
14.
Phys Rev E Stat Nonlin Soft Matter Phys ; 83(5 Pt 1): 051108, 2011 May.
Article in English | MEDLINE | ID: mdl-21728491

ABSTRACT

Population dynamics in systems composed of cyclically competing species has been of increasing interest recently. Here we investigate a system with four or more species. Using mean field theory, we study in detail the trajectories in configuration space of the population fractions. We discover a variety of orbits, shaped like saddles, spirals, and straight lines. Many of their properties are found explicitly. Most remarkably, we identify a collective variable that evolves simply as an exponential: Q ∝ e(λt), where λ is a function of the reaction rates. It provides information on the state of the system for late times (as well as for t→-∞). We discuss implications of these results for the evolution of a finite, stochastic system. A generalization to an arbitrary number of cyclically competing species yields valuable insights into universal properties of such systems.


Subject(s)
Models, Theoretical , Population Dynamics , Biological Evolution , Extinction, Biological , Stochastic Processes
17.
Phys Rev E Stat Nonlin Soft Matter Phys ; 80(3 Pt 1): 031142, 2009 Sep.
Article in English | MEDLINE | ID: mdl-19905097

ABSTRACT

Using Monte Carlo simulations and a domain-wall theory, we discuss the effect of coupling several totally asymmetric simple exclusion processes (TASEPs) to a finite reservoir of particles. This simple model mimics directed biological transport processes in the presence of finite resources such as protein synthesis limited by a finite pool of ribosomes. If all TASEPs have equal length, we find behavior which is analogous to a single TASEP coupled to a finite pool. For the more generic case of chains with different lengths, several unanticipated regimes emerge. A generalized domain-wall theory captures our findings in good agreement with simulation results.

18.
Phys Rev E Stat Nonlin Soft Matter Phys ; 79(4 Pt 2): 046104, 2009 Apr.
Article in English | MEDLINE | ID: mdl-19518298

ABSTRACT

We revisit the classical model for voter dynamics in a two-party system with two basic modifications. In contrast to the original voter model studied in regular lattices, we implement the opinion formation process in a random network of agents in which interactions are no longer restricted by geographical distance. In addition, we incorporate the rapidly changing nature of the interpersonal relations in the model. At each time step, agents can update their relationships. This update is determined by their own opinion, and by their preference to make connections with individuals sharing the same opinion, or rather with opponents. In this way, the network is built in an adaptive manner, in the sense that its structure is correlated and evolves with the dynamics of the agents. The simplicity of the model allows us to examine several issues analytically. We establish criteria to determine whether consensus or polarization will be the outcome of the dynamics and on what time scales these states will be reached. In finite systems consensus is typical, while in infinite systems a disordered metastable state can emerge and persist for infinitely long time before consensus is reached.

19.
Phys Rev E Stat Nonlin Soft Matter Phys ; 80(6 Pt 1): 061602, 2009 Dec.
Article in English | MEDLINE | ID: mdl-20365176

ABSTRACT

Motivated by a series of experiments that revealed a temperature dependence of the dynamic scaling regime of growing surfaces, we investigate theoretically how a nonequilibrium growth process reacts to a sudden change of system parameters. We discuss quenches between correlated regimes through exact expressions derived from the stochastic Edwards-Wilkinson equation with a variable diffusion constant. Our study reveals that a sudden change of the diffusion constant leads to remarkable changes in the surface roughness. Different dynamic regimes, characterized by a power-law or by an exponential relaxation, are identified, and a dynamic phase diagram is constructed. We conclude that growth processes provide one of the rare instances where quenches between correlated regimes yield a power-law relaxation.


Subject(s)
Crystallization/methods , Macromolecular Substances/chemistry , Models, Chemical , Computer Simulation , Surface Properties
20.
Postgrad Med J ; 83(986): 738, 2007 Dec.
Article in English | MEDLINE | ID: mdl-18057170

ABSTRACT

The implementation of modernizing medical careers (MMC) has resulted in some specialties being allocated very inexperienced trainees such as ophthalmology. We aim to describe the process of implementation of MMC and how it may affect the service provision in smaller specialities such as ophthalmology. A methodical approach in a district hospital setting was used to provide early core training to such trainees involving managerial support. The quality of service provided by newer trainees can be enhanced by providing early structured training during induction to create an atmosphere of enthusiasm and continued learning. This example can be used in other units and specialties.


Subject(s)
Education, Medical, Graduate/methods , Medical Staff, Hospital/education , Ophthalmology/education , England , Humans
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