2,174 research outputs found
Generalized phase-space kinetic and diffusion equations for classical and dispersive transport
We formulate and solve a physically-based, phase space kinetic equation for transport in the presence of trapping. Trapping is incorporated through a waiting time distribution function. From the phase-space analysis, we obtain a generalized diffusion equation in configuration space. We analyse the impact of the waiting time distribution, and give examples that lead to dispersive or non-dispersive transport. With an appropriate choice of the waiting time distribution, our model is related to fractional diffusion in the sense that fractional equations can be obtained in the limit of long times. Finally, we demonstrate the application of this theory to disordered semiconductors
A fourteen-year review of breast pathology at a rural referral center in western Kenya
Background: Breast cancer has a low incidence in Africa compared with other continents. Of breast cancer reported in Africa, middle and eastern Africa is reported with the lowest incidence. In general, there is a paucity of information about breast cancer in Africa. Breast cancer evaluation and treatment is plagued with inadequate resource and screening facility throughout sub-Saharan Africa. Therefore, it is difficult to adequately assess incidence or prevalence without appropriate cancer or death registries. To our knowledge, no data exists for breast cancer treated in rural Kenya.Methods: Review of all surgical pathology reports was performed from January 31, 1993 to August 31, 2007 at Tenwek Hospital, a 300 bed referral center located in Bomet, Kenya. Records were searched for any breast specimen or specimen related to breast disease such as metastatic breast disease.Results: For the studied period, a total of 118 breast cancers were identified from pathology report records. Men accounted for 13 (11.02%) of all breast cancers. The average age for men was 69 years (std 10.6). The average age of women (n=105) was 51.2 years (std 15.6). The difference between the mean ages among men and women was statistically significant (p=0.000195). Grades were listed for only 55 of 118 specimens. Grade 3 was recorded in 61.8% (34/55). Women, aged 50 years or less, comprised 59.3% of all women recorded ages. In females, Grade 1 occurred in 7.1%, Grade 2 in 39.3%, and Grade 3 in 53.6%. Average age for Grade 1 histology is 37.5 years (std 2.1), Grade 2 average was 38.3 years (std 5.9) and Grade 3 average age was 40.8 years (std 5.7). The majority of males had IDC (12/13) with one case of NHL and melanoma of the breast
Boltzmann's equation at 150: Traditional and modern solution techniques for charged particles in neutral gases
Seminal gas discharge experiments of the late 19th and early 20th centuries laid the foundations of modern physics, and the influence of this "golden era" continues to resonate well into the 21st century through modern technologies, medical applications, and fundamental scientific investigations. Key to this continuing success story has been the kinetic equation formulated by Ludwig Boltzmann in 1872, which provides the theoretical foundations necessary for analyzing such highly non-equilibrium situations. However, as discussed here, the full potential of Boltzmann's equation has been realized only in the past 50 years or so, with modern computing power and analytical techniques facilitating accurate solutions for various types of charged particles (ions, electrons, positrons, and muons) in gases. Our example of thermalization of electrons in xenon gas highlights the need for such accurate methods-the traditional Lorentz approximation is shown to be hopelessly inadequate. We then discuss the emerging role of Boltzmann's equation in determining cross sections by inverting measured swarm experiment transport coefficient data using machine learning with artificial neural networks
The Importance of Economic Perspective and Quantitative Approaches in Oncology Value Frameworks of Drug Selection and Shared Decision Making
The debate around value in oncology drug selection has been prominent in
recent years, and several professional bodies have furthered this debate
by advocating for so-called value frameworks. Herein, we provide a viewpoint
on these value frameworks, emphasizing the need to consider 4 key
aspects: (1) the economic underpinnings of value; (2) the importance of
the perspective adopted in the valuation; (3) the importance of the difference
between absolute and relative measures of risk and measuring
patient preferences; and (4) the recognition of multiple quality-of-life (QoL)
domains, and the aggregation and valuation of those domains, through
utilities within a multicriteria decision analysis, may allow prioritization of
QoL above the tallying of safety events, particularly in a value framework
focusing on the individual patient.
While several frameworks exist, they incorporate different attributes
and—importantly—assess value from alternative perspectives, including
those of patients, regulators, payers, and society. The various perspectives
necessarily lead to potentially different, if not sometimes divergent, conclusions
about the valuation. We show that the perspective of the valuation
affects the framing of the risk/benefit question and the methodology to
measure the individual patient choice, or preference, as opposed to the
collective, or population, choice.
We focus specifically on the American Society of Clinical Oncology
(ASCO) Value Framework. We argue that its laudable intent to assist in
shared clinician-patient decision making can be augmented by more formally
adopting methodology underpinned by micro- and health economic
concepts, as well as application of formal quantitative approaches. Our recommendations
for value frameworks focusing on the individual patient, such
as the ASCO Value Framework, are 3-fold: (1) ensure that stakeholders
understand the importance of the adopted (economic) perspective; (2)
consider using exclusively absolute measures of risk and formal patientpreference
methodology; and (3) consider foregoing safety parameters for
higher-order utility considerations
On the approximation of transport properties in structured materials using momentum-transfer theory
In this paper, we present a fluid model for electrons and positrons in structured and soft-condensed matter utilizing dilute gas phase cross-sections together with a structure factor for the medium. Generalizations of the Wannier energy and Einstein (Nernst–Townsend) relations to account for coherent scattering effects present in soft-condensed matter are presented along with new expressions directly relating transport properties in the dilute gas and the structured matter phases. The theory is applied to electrons in a benchmark Percus–Yevick model and positrons in liquid argon, and the accuracy is tested against a multi-term solution of Boltzmann's equation (White and Robson 2011 Phys. Rev. E 84 031125)
Domestic Rivalry and Export Performance: Theory and Evidence from International Airline Markets
The much-studied relationship between domestic rivalry and export performance consists of those supporting a national-champion rationale, and those supporting a rivalry rationale. While the empirical literature generally supports the positive effects of domestic rivalry, the national-champion rationale actually rests on firmer theoretical ground. We address this inconsistency by providing a theoretical framework that illustrates three paths via which domestic rivalry translates into enhanced international exports. Furthermore, empirical tests on the world airline industry elicit the existence of one particular path - an enhanced firm performance effect - that connects domestic rivalry with improved international exports
Kinematic characteristics of elite men's 50 km race walking.
Race walking is an endurance event which also requires great technical ability, particularly with respect to its two distinguishing rules. The 50 km race walk is the longest event in the athletics programme at the Olympic Games. The aims of this observational study were to identify the important kinematic variables in elite men's 50 km race walking, and to measure variation in those variables at different distances. Thirty men were analysed from video data recorded during a World Race Walking Cup competition. Video data were also recorded at four distances during the European Cup Race Walking and 12 men analysed from these data. Two camcorders (50 Hz) recorded at each race for 3D analysis. The results of this study showed that walking speed was associated with both step length (r=0.54,P=0.002) and cadence (r=0.58,P=0.001). While placing the foot further ahead of the body at heel strike was associated with greater step lengths (r=0.45,P=0.013), it was also negatively associated with cadence (r= -0.62,P<0.001). In the World Cup, knee angles ranged between 175 and 186° at initial contact and between 180 and 195° at midstance. During the European Cup, walking speed decreased significantly (F=9.35,P=0.002), mostly due to a decrease in step length between 38.5 and 48.5 km (t=8.59,P=0.014). From this study, it would appear that the key areas a 50 km race walker must develop and coordinate are step length and cadence, although it is also important to ensure legal walking technique is maintained with the onset of fatigue
Metal-insulator transition in the one-dimensional Holstein model at half filling
We study the one-dimensional Holstein model with spin-1/2 electrons at
half-filling. Ground state properties are calculated for long chains with great
accuracy using the density matrix renormalization group method and extrapolated
to the thermodynamic limit. We show that for small electron-phonon coupling or
large phonon frequency, the insulating Peierls ground state predicted by
mean-field theory is destroyed by quantum lattice fluctuations and that the
system remains in a metallic phase with a non-degenerate ground state and
power-law electronic and phononic correlations. When the electron-phonon
coupling becomes large or the phonon frequency small, the system undergoes a
transition to an insulating Peierls phase with a two-fold degenerate ground
state, long-range charge-density-wave order, a dimerized lattice structure, and
a gap in the electronic excitation spectrum.Comment: 6 pages (LaTex), 10 eps figure
Fluctuating Elastic Rings: Statics and Dynamics
We study the effects of thermal fluctuations on elastic rings. Analytical
expressions are derived for correlation functions of Euler angles, mean square
distance between points on the ring contour, radius of gyration, and
probability distribution of writhe fluctuations. Since fluctuation amplitudes
diverge in the limit of vanishing twist rigidity, twist elasticity is essential
for the description of fluctuating rings. We find a crossover from a small
scale regime in which the filament behaves as a straight rod, to a large scale
regime in which spontaneous curvature is important and twist rigidity affects
the spatial configurations of the ring. The fluctuation-dissipation relation
between correlation functions of Euler angles and response functions, is used
to study the deformation of the ring by external forces. The effects of inertia
and dissipation on the relaxation of temporal correlations of writhe
fluctuations, are analyzed using Langevin dynamics.Comment: 43 pages, 9 Figure
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