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PubMed2000

Personal exposure to atmospheric polycyclic aromatic hydrocarbons in a general adult population and lung cancer risk assessment.

Personal exposure to nine particulate-phase atmospheric polycyclic aromatic hydrocarbons (PAHs) was assessed among adult non-smoking volunteers in the Grenoble, France, metropolitan area. Using Toxic Equivalency Factors, the associated total atmospheric PAHs lifelong cancer risk was estimated. For 48 hours continuously, 38 subjects without specific occupational exposure to combustion sources carried a PM2.5 particles personal exposure monitor while at home, at work, commuting, or involved in other activities. One phase of the study took place in summer; a second in winter. The monitor set was composed of a pump with an airflow of 4 L.mn-1, a 2.5-micron cyclone, and Teflon filters. The PAH concentrations were determined on seven PM2.5 filters by using high performance liquid chromatography with fluorimetric detection. The predominant PAHs are fluoranthene and indeno pyrene. According to the compound, the personal exposure estimates ranged from 0.13 to 1.67 ng/m3 (yearly means). The average benzo(a) pyrene value is 0.67 ng/m3 (95% confidence interval = 0 to 2.1 ng/m3). Winter exposures were 3 to 25 times greater than summer exposures. The total PAHs lung cancer lifelong risk is 7.8 10(-5) and is driven by exposure to benzo(a) pyrene. Although these risk estimates are 2 to 3 orders of magnitude lower than those associated with specific occupational exposures in the coal or smelter industries, they are of public health concern because they are spread over large urban populations. Further personal exposure studies in adult or children populations are needed.

Adult↗
PubMedDate not supplied

The local public health workforce in rural communities.

This work describes the public health workforce and training needs of rural local public health agencies (LPHAs) in comparison with suburban and metropolitan LPHA jurisdictions. A survey was sent to 1,100 LPHAs nationwide. The rural urban commuting area codes (RUCAs) defined LPHAs as rural or urban, and the Standard Occupational Classification system enumerated the workforce. Most occupational classifications had significantly fewer staff in rural LPHAs. Public health nurses ranked as the most needed staff and serve in various important capacities in rural LPHAs. In terms of training, job-specific or programmatic continuing education was identified as the most important training need. Developing leadership and public health workforce capacity within rural public health is an essential agenda item for rural America. Decision makers may need to consider different organizational structures while balancing the need for local input and control. Regionalization and collaborative approaches to difficult workforce issues may present potential solutions to workforce challenges.

Employment↗
PubMed2005

Casualties treated at the closest hospital in the Madrid, March 11, terrorist bombings.

BACKGROUND: At 07:39 am on March 11th, 2004, ten terrorist bomb explosions occurred almost simultaneously in four commuter trains in Madrid, Spain, killing instantly 177 people and injuring >2,000. There were 14 subsequent in-hospital deaths, bringing the definite death toll to 191 victims. This article describes the organization of the clinical management and patterns of injuries in casualties who were taken to the closest hospital, with emphasis on the critical patient population. RESULTS: There were 312 patients taken to that center, and 91 were hospitalized, 89 of them (28.5%) for >24 hrs. Sixty-two patients only had superficial bruises or emotional shock, but the remaining 250 patients had more severe lesions. The data on 243 of the latter form the basis of this report. Tympanic perforation occurred in 41% of 243 victims with moderate-to-severe trauma, chest injuries in 40%, shrapnel wounds in 36%, fractures in 18%, first- or second-degree burns in 18%, eye lesions in 18%, head trauma in 12%, and abdominal injuries in 5%. Between 8:00 am and 5:00 pm, 34 surgical interventions were performed on 32 victims. Twenty-nine casualties (12% of the total or 32.5% of those hospitalized) were deemed in critical condition, and two of them died within minutes of arrival. The other 27 survived to be admitted to intensive care units, and three of them died, bringing the critical mortality rate to 17.2% (5/29). The mean Injury Severity Score and Acute Physiology and Chronic Health Evaluation II scores of critical patients were 34 and 23, respectively. Among these critical patients, soft-tissue and musculoskeletal injuries predominated in 85% of cases, ear blast injury was identified in 67%, and blast lung injury was present in 63% (17 cases). Fifty-two percent suffered head trauma. CONCLUSIONS: There was probably an overtriage to the closest hospital, and the time of the blasts proved crucial for the adequacy of the medical and surgical response. The number of blast lung injuries seen is probably the largest reported by a single institution, and the critical mortality rate was reasonably low.

Blast Injuries↗
PubMed2006

Will improvement in quality of life (QOL) impact fatigue in patients receiving radiation therapy for advanced cancer?

BACKGROUND: Fatigue has a significant impact on the quality of life (QOL) of cancer patients. Recent research has suggested that physical activity can reduce fatigue in patients receiving active cancer treatment. In this project, we examined the impact that participation in a randomized controlled trial of a multidisciplinary intervention designed to impact overall QOL had on fatigue for advanced cancer patients actively receiving treatment. METHODS: Patients with newly diagnosed cancer were randomly assigned to an 8-session structured multidisciplinary intervention or a standard-care arm at the beginning of their course of radiotherapy (RT) designed to impact QOL. Ninety-minute sessions were led by either a psychiatrist or psychologist, collaborating with a nurse, physical therapist, chaplain, or social worker, depending on the session's theme. The fatigue assessments used in this trial included the Linear Analogue Self Assessment (LASA), the Profile of Mood States (POMS), Spielberger's State-Trait Anxiety Inventory (STAI), and the Symptom Distress Scale (SDS). RESULTS: There were 115 participants enrolled and the 2 randomization arms were well balanced in terms of baseline characteristics and treatment received except for increased commuting distance for the patients in the intervention arm (P = 0.042). Most of scores indicated less fatigue (higher score) in the standard treatment group, but there were no statistically significant differences found at baseline and weeks 4, 8, and 27 except for SDS at week 8 (P = 0.018) with less patients reporting significant fatigue in the standard treatment arm. For the entire participant population, fatigue levels initially worsened with radiotherapy, stabilized at week 8, and returned to baseline by week 27. Disease site, chemotherapy use, and radiotherapy dose did not have a significant impact on fatigue levels. CONCLUSIONS: Radiotherapy initially caused a worsening of fatigue but with time fatigue levels returned to baseline. Clinically, this structured multidisciplinary intervention had no impact on fatigue, and there was the suggestion the multiple sessions may have contributed to worse fatigue during active cancer treatment.

Adult↗
PubMed2003

Antecedents and consequences of work-family conflict: a prospective cohort study.

This study examined both risk factors for the onset of work-family conflict and consequences in terms of need for recovery and prolonged fatigue for men and women separately. Two-year follow-up data from the Maastricht Cohort Study on "Fatigue at Work" (n = 12,095) were used. At baseline, the prevalence of work-family conflict was 10.8% (9.0% in women; 11.1% in men), the cumulative incidence at 1 year follow-up was 5.1%. For men, several work-related demands, shift work, job insecurity, conflicts with coworkers or supervisor, having full responsibility for housekeeping, and having to care for a chronically ill child or other family member at home were risk factors for the onset of work-family conflict, whereas decision latitude and coworker and supervisor social support protected against work-family conflict. In women, physical demands, overtime work, commuting time to work, and having dependent children were risk factors for work-family conflict, whereas domestic help protected against work-family conflict at 1 year follow-up. Work-family conflict was further shown to be a strong risk factor for the onset of elevated need for recovery from work and fatigue.

Adult↗
PubMed2003

Scale-dependent hierarchical adjustments of movement patterns in a long-range foraging seabird.

Foraging animals are expected to adjust their path according to the hierarchical spatial distribution of food resources and environmental factors. Studying such behaviour requires methods that allow for the detection of changes in pathways' characteristics across scales, i.e. a definition of scale boundaries and techniques to continuously monitor the precise movement of the animal over a sufficiently long period. We used a recently developed application of fractals, the changes in fractal dimension within a path and applied it to foraging trips over scales ranging across five orders of magnitude (10 m to 1000 km), using locations of wandering albatrosses (Diomedea exulans) recorded at 1 s intervals with a miniaturized global positioning system. Remarkably, all animals consistently showed the same pattern: the use of three scale-dependent nested domains where they adjust tortuosity to different environmental and behavioural constraints. At a small scale (ca. 100 m) they use a zigzag movement as they continuously adjust for optimal use of wind; at a medium scale (1-10 km), the movement shows changes in tortuosity consistent with food-searching behaviour; and at a large scale (greater than 10 km) the movement corresponds to commuting between patches and is probably influenced by large-scale weather systems. Our results demonstrate the possibility of identifying the hierarchical spatial scales at which long-ranging animals adjust their foraging behaviour, even in featureless environments such as oceans, and hence how to relate their movement patterns to environmental factors using an objective mathematical approach.

Animals↗
PubMed2025

A Systematic Review of Spatial Epidemiological Modeling Approaches Applied During the COVID-19 Pandemic.

BACKGROUND: A wide range of epidemiological modeling approaches have been applied to the SARS-CoV-2 pandemic, which presents an opportunity to assess common approaches applied to specific research questions. Spatial models interrogate how heterogeneities and host movement dynamics influence local and regional patterns of disease, issues that were of great interest for understanding and controlling SARS-CoV-2. OBJECTIVE: Here we present a systematic review of spatial epidemiological modeling approaches of SARS-CoV-2. We describe common themes and highlight unique strategies, providing a foundation for researchers to devise spatial models most appropriate for future pathogens and epidemics. Our review also categorizes the research questions that were addressed with spatial models, highlights parameter estimation techniques, and describes the cyber infrastructure used for model development. METHODS: We conducted a systematic review using Web of Science and a standardized set of keywords, followed by thorough examination of abstracts and full texts to determine which studies met our inclusion criteria. To guide our description and comparisons of models, we developed a Geography, Population, Movement (GPM) framework that conceptualizes the interactions between three distinct subcomponents of any spatial model. The geographic model represents the physical arena in which the model is implemented, the intra-population model describes the transmission and disease processes that occur within distinct spatial units of the geography, and the movement model describes the algorithms that dictate how hosts move among spatial units within the geography. RESULTS: The search identified a total of 193 articles, of which 109 were included in our review. The most abundant intra-population modeling methods were agent-based (47.7%) and compartmental modeling (29.4%) approaches. Movement models ranged in complexity, with the most complex models implementing commuter movement among many points of interest in the geographic arena, which were sometimes parameterized by fine-scale mobility data. Geographic models ranged from describing microcosms, such as single classrooms, all the way up to multi-country models. Of the 63.3% of models studies that specified the programming language used, we detected ten different languages, with Matlab and Python being the most frequent, although only 30.6% of studies provided open-access code for their models. We also described eight specialized software systems that were used to construct agent-based or compartment models of COVID-19. CONCLUSIONS: Our review identified and characterized a variety of spatial modeling strategies and software that were usefully employed to address many relevant epidemiological questions for COVID-19. Future research is needed to quantitatively assess which modeling approaches are most appropriate in specific situations, to answer specific questions, or to apply to certain disease systems. Moreover, future cyberinfrastructure could help to modularize and standardize modeling approaches, which would increase transparency and reproducibility, and which would facilitate a detailed examination of which model attributes relate to model performance in a variety of contexts.

COVID-19↗
PubMed1999

Unified algebraic Bethe ansatz for two-dimensional lattice models.

We develop a unified formulation of the quantum inverse scattering method for lattice vertex models associated to the nonexceptional A(2)(2r), A(2)(2r-1), B(1)(r), C(1)(r), D(1)(r+1), and D(2)(r+1) Lie algebras. We recast the Yang-Baxter algebra in terms of different commutation relations between creation, annihilation, and diagonal fields. The solution of the D(2)(r+1) model is based on an interesting 16-vertex model, which is solvable without recourse to a Bethe ansatz.

Journal Article↗
PubMed1999

Power-law distributions and Lévy-stable intermittent fluctuations in stochastic systems of many autocatalytic elements.

A generic model of stochastic autocatalytic dynamics with many degrees of freedom w(i,) i=1, em leader,N, is studied using computer simulations. The time evolution of the w(i)'s combines a random multiplicative dynamics w(i)(t+1)=lambdaw(i)(t) at the individual level with a global coupling through a constraint which does not allow the w(i)'s to fall below a lower cutoff given by cw, where w is their momentary average and 0 infinity and the limit of decoupled free multiplicative random walks c-->0 do not commute: alpha(0,N)=0 for any finite N while alpha(c,infinity)>or=1 (which is the common range in empirical systems) for any positive c. The time evolution of w(t) exhibits intermittent fluctuations parametrized by a (truncated) Lévy-stable distribution L(alpha)(r) with the same index alpha. This nontrivial relation between the distribution of the wi's at a given time and the temporal fluctuations of their average is examined, and its relevance to empirical systems is discussed.

Journal Article↗
PubMed2000

Path-integral formulation of stochastic processes for exclusive particle systems

We present a systematic formalism to derive a path-integral formulation for hard-core particle systems far from equilibrium. Writing the master equation for a stochastic process of the system in terms of the annihilation and creation operators with mixed commutation relations, we find the Kramers-Moyal coefficients for the corresponding Fokker-Planck equation (FPE), and the stochastic differential equation (SDE) is derived by connecting these coefficients in the FPE to those in the SDE. Finally, the SDE is mapped onto field theory using the path integral, giving the field-theoretic action, which may be analyzed by the renormalization group method. We apply this formalism to a two-species reaction-diffusion system with drift, finding a universal decay exponent for the long-time behavior of the average concentration of particles in arbitrary dimension.

Journal Article↗
PubMed2000

Fourth-order algorithms for solving the multivariable Langevin equation and the Kramers equation.

We develop a fourth-order simulation algorithm for solving the stochastic Langevin equation. The method consists of identifying solvable operators in the Fokker-Planck equation, factorizing the evolution operator for small time steps to fourth order, and implementing the factorization process numerically. A key contribution of this paper is to show how certain double commutators in the factorization process can be simulated in practice. The method is general, applicable to the multivariable case, and systematic, with known procedures for doing fourth-order factorizations. The fourth-order convergence of the resulting algorithm allowed very large time steps to be used. In simulating the Brownian dynamics of 121 Yukawa particles in two dimensions, the converged result of a first-order algorithm can be obtained by using time steps 50 times as large. To further demonstrate the versatility of our method, we derive two new classes of fourth-order algorithms for solving the simpler Kramers equation without requiring the derivative of the force. The convergence of many fourth-order algorithms for solving this equation are compared.

Journal Article↗
PubMed2001

Simplifying Kaufman's solution of the two-dimensional Ising model.

We considerably simplify Kaufman's solution of the two-dimensional Ising model by introducing two commuting representations of the complex rotation group SO(2n,C). All eigenvalues of the transfer matrix and therefore the partition function are found in a straightforward way.

Journal Article↗
PubMed2002

Canonical Hamiltonian formulation of the nonlinear Schrödinger equation in a one-dimensional, periodic Kerr medium.

A canonical Hamiltonian formulation of the nonlinear Schrödinger equation has been derived in this paper. This formulation governs the dynamics of pulse propagation in a one-dimensional, periodic Kerr medium when the frequency content of the pulse is sufficiently narrow relative to a carrier frequency, and sufficiently far removed from a photonic band gap of the medium. Our Hamiltonian is numerically equal to the energy, and our fields obey canonical commutation relations, so the theory can easily be quantized. We clarify the nature of the conserved quantities associated with simple symmetries.

Journal Article↗
PubMed2002

Discrete four-stroke quantum heat engine exploring the origin of friction.

The optimal power performance of a first-principle quantum heat engine model shows friction-like phenomena when the internal fluid Hamiltonian does not commute with the external control field. The model is based on interacting two-level systems where the external magnetic field serves as a control variable.

Journal Article↗
PubMed2002

Stochastic instability of quasi-isolated systems.

The stability of solutions to evolution equations with respect to small stochastic perturbations is considered. The stability of a stochastic dynamical system is characterized by the local stability index. The limit of this index with respect to infinite time describes the asymptotic stability of a stochastic dynamical system. Another limit of the stability index is given by the vanishing intensity of stochastic perturbations. A dynamical system is stochastically unstable when these two limits do not commute with each other. Several examples illustrate the thesis that there always exist such stochastic perturbations that render a given dynamical system stochastically unstable. The stochastic instability of quasi-isolated systems is responsible for the irreversibility of time arrow.

Journal Article↗
PubMed2002

Energy-momentum spectrum of some two-particle lattice Schrödinger Hamiltonians.

We determine the excitation spectrum of some one and two-particle Z(d) lattice Schrödinger Hamiltonians. They occur as approximate Hamiltonians for the low-lying energy-momentum spectrum of diverse infinite lattice nonlinear quantum systems. A unitary staggering transformation relates the low-energy-momentum spectrum to the high-energy-momentum spectrum of the transformed operators. A feature for the one-particle repulsive delta function Hamiltonian is that, in addition to the continuous band spectrum, there is a bound state above the band, and the repulsive case spectrum and scattering can be obtained from the attractive potential case by staggering. For the two-particle pair potential Hamiltonian, there are commuting self-adjoint energy-momentum operators, and we determine the joint spectrum. For the case of a lambda delta pair potential, and equal particle masses, for arbitrarily small /lambda/, lambda < 0, and d >or = 3, there is no bound state for small system momentum, but a bound state exists below the band if the momentum is large. We find that the binding energy is an increasing function of the system momentum. The existence of this bound state is in contrast with the continuum case, where the Birman-Schwinger bound excludes negative-energy bound states for small couplings; this bound state is absent if the two masses are different. Other spectral results are also obtained for the large coupling case. An eigenfunction expansion that uses products of plane waves in the sum and difference coordinates is used to obtain the spectral results.

Journal Article↗
PubMed2003

Bilinear diffusion quantum Monte Carlo methods.

The standard method of quantum Monte Carlo for the solution of the Schrödinger equation in configuration space can be described quite generally as devising a random walk that generates-at least asymptotically-populations of random walkers whose probability density is proportional to the wave function of the system being studied. While, in principle, the energy eigenvalue of the Hamiltonian can be calculated with high accuracy, estimators of operators that do not commute the Hamiltonian cannot. Bilinear quantum Monte Carlo (BQMC) is an alternative in which the square of the wave function is sampled in a somewhat indirect way. More specifically, one uses a pair of walkers at positions x and y and introduces stochastic dynamics to sample phi(i)(x)t(x,y)phi(j)(y), where phi(i)(x) and phi(j)(y) are eigenfunctions of (possibly different) Hamiltonians, and t(x,y) is a kernel that correlates positions x and y. Using different Hamiltonians permits the accurate computation of small energy differences. We review the conceptual basis of BQMC, discuss qualitatively and analytically the problem of the fluctuations in the branching, and present partial solutions to that problem. Finally we exhibit numerical results for some model systems including harmonic oscillators and the hydrogen and helium atoms. Further research will be necessary to make this a practical and generally applicable scheme.

Journal Article↗
PubMed2003

Quantum four-stroke heat engine: thermodynamic observables in a model with intrinsic friction.

The fundamentals of a quantum heat engine are derived from first principles. The study is based on the equation of motion of a minimum set of operators, which is then used to define the state of the system. The relation between the quantum framework and the thermodynamical observables is examined. A four-stroke heat engine model with a coupled two-level system as a working fluid is used to explore the fundamental relations. In the model used, the internal Hamiltonian does not commute with the external control field, which defines the two adiabatic branches. Heat is transferred to the working fluid by coupling to hot and cold reservoirs under constant field values. Explicit quantum equations of motion for the relevant observables are derived on all branches. The dynamics on the heat transfer constant field branches is solved in closed form. On the adiabats, a general numerical solution is used and compared with a particular analytic solution. These solutions are combined to construct the cycle of operation. The engine is then analyzed in terms of the frequency-entropy and entropy-temperature graphs. The irreversible nature of the engine is the result of finite heat transfer rates and frictionlike behavior due to noncommutability of the internal and external Hamiltonians.

Journal Article↗