4,501 research outputs found
Octonic Electrodynamics
In this paper we present eight-component values "octons", generating
associative noncommutative algebra. It is shown that the electromagnetic field
in a vacuum can be described by a generalized octonic equation, which leads
both to the wave equations for potentials and fields and to the system of
Maxwell's equations. The octonic algebra allows one to perform compact combined
calculations simultaneously with scalars, vectors, pseudoscalars and
pseudovectors. Examples of such calculations are demonstrated by deriving the
relations for energy, momentum and Lorentz invariants of the electromagnetic
field. The generalized octonic equation for electromagnetic field in a matter
is formulated.Comment: 12 pages, 1 figur
Sorting of multiple molecular species on cell membranes
Eukaryotic cells maintain their inner order by a hectic process of
distillation of molecular factors taking place on the surface of their lipid
membranes. To understand the properties of this molecular sorting process, a
physical model of the process has been recently proposed [arXiv:1811.06760],
based on (a) the phase separation of a single, initially dispersed molecular
species into spatially localized sorting domains on the lipid membrane, and (b)
domain-induced membrane bending leading to the nucleation of submicrometric
lipid vesicles, naturally enriched in the molecules of the engulfed sorting
domain. The analysis of the model has shown the existence of an optimal region
of the parameter space where sorting is most efficient. Here, the model is
extended to account for the simultaneous distillation of a pool of distinct
molecular species. We find that the mean time spent by sorted molecules on the
membrane increases with the heterogeneity of the pool (i.e., the number of
distinct molecular species sorted) according to a simple scaling law, and that
a large number of distinct molecular species can in principle be sorted in
parallel on a typical cell membrane region without significantly interfering
with each other. Moreover, sorting is found to be most efficient when the
distinct molecular species have comparable homotypic affinities. We also
consider how valence (i.e., the average number of interacting neighbors of a
molecule in a sorting domain) affects the sorting process, finding that
higher-valence molecules can be sorted with greater efficiency than
lower-valence molecules
Masculinity and feminity measurement in physical education teachers
Esta investigación tuvo por objetivo analizar las mediciones de masculinidad,
feminidad, machismo y sumisión, características asociadas a la personalidad, de un
grupo de docentes de Educación Física. Participaron en el estudio 53 docentes de
nivel básico que laboran en un programa implementado por una institución
gubernamental en la Ciudad de México. El muestreo fue de tipo no probabilístico.
Se empleó como instrumento el Inventario de Masculinidad y Feminidad (IMAFE),
instrumento confiable y válido en México, sujeto a prueba en otros países, en él se
incluyen aspectos de los papeles de género tradicionales: machismo y sumisión. El
análisis de los datos se efectúo mediante la prueba “t-Student” y el análisis de
varianza de una clasificación, así como la comparación de medias de los resultados
arrojados. Se concluye que no hay diferencias estadísticamente significativas en las
cuatro escalas propuestas por el IMAFE y las variables de trabajo, sexo, edad y
estado civil, en el grupo de docentes de Educación Física, en lo que respecta a las
características asociadas a la personalidadThis research aimed to analyze the measurements of masculinity, femininity,
machismo and submission features associated with the personality characteristics
of a group of physical education teachers. Participated in the study53 basic level
teachers working in a program implemented by a government institution in Mexico
City. The sampling was not probabilistic type. As a tool for data collection was used
the Inventory of Masculinity and femininity (IMAFE), reliable and valid instrument in
Mexico, subject to testing in other countries, there aspects of traditional gender
roles: machismo and submission. Data analysis undertaken using the “t-student”
test and analysis of variance classification and comparison of the results obtained.
It is concluded that no statistically significant differences in the four scales
proposed by IMAFE and work variables sex, age and marital status in the group of
physical education teachers in regard to the characteristics associated with
personalit
Universal features of cell polarization processes
Cell polarization plays a central role in the development of complex
organisms. It has been recently shown that cell polarization may follow from
the proximity to a phase separation instability in a bistable network of
chemical reactions. An example which has been thoroughly studied is the
formation of signaling domains during eukaryotic chemotaxis. In this case, the
process of domain growth may be described by the use of a constrained
time-dependent Landau-Ginzburg equation, admitting scale-invariant solutions
{\textit{\`a la}} Lifshitz and Slyozov. The constraint results here from a
mechanism of fast cycling of molecules between a cytosolic, inactive state and
a membrane-bound, active state, which dynamically tunes the chemical potential
for membrane binding to a value corresponding to the coexistence of different
phases on the cell membrane. We provide here a universal description of this
process both in the presence and absence of a gradient in the external
activation field. Universal power laws are derived for the time needed for the
cell to polarize in a chemotactic gradient, and for the value of the smallest
detectable gradient. We also describe a concrete realization of our scheme
based on the analysis of available biochemical and biophysical data.Comment: Submitted to Journal of Statistical Mechanics -Theory and Experiment
Estimation of User's Orientation via Wearable UWB
User's orientation in indoor environments is an important part of her context. Orientation can be useful to understand what the user is looking at, and thus to improve the interaction between her and the surrounding environment. In this paper, we present a method based on wearable UWB-enabled devices. The position of the devices in space is used to estimate the user's orientation. We experimentally evaluated the impact of some operational parameters, such as the distance between worn devices, or some environmental conditions, such as the position of the user in the room. Results show that the accuracy of the method suits the needs of a wide range of practical purposes
Pathogenic Aβ A2V versus protective Aβ A2T mutation : early stage aggregation and membrane interaction
We investigated the effects of punctual A-to-V and A-to-T mutations in the amyloid precursor protein APP, corresponding to position 2 of A\u3b21\u201342. Those mutations had opposite effects on the onset and progression of Alzheimer disease, the former inducing early AD pathology and the latter protecting against the onset of the disease. We applied Static and Dynamic Light Scattering and Circular Dichroism, to study the different mutants in the early stages of the aggregation process, essential for the disease. Comparative results showed that the aggregation pathways differ in the kinetics and extent of the process, in the size of the aggregates and in the evolution of the secondary structure, resulting in fibrils of different morphology, as seen by AFM. Mutated peptides had comparable toxic effects on N2a cells. Moreover, as assessed by X-ray scattering, all of them displayed disordering effects on the internal structure of mixed phospholipids-gangliosides model membranes
Statistics of the One-Electron Current in a One-Dimensional Mesoscopic Ring at Arbitrary Magnetic Fields
The set of moments and the distribution function of the one-electron current
in a one-dimensional disordered ring with arbitrary magnetic flux are
calculated.Comment: 10 pages; Plain TeX; IFUM 448/FT; to appear in J. Stat. Phy
The dissipative linear Boltzmann equation for hard spheres
We prove the existence and uniqueness of an equilibrium state with unit mass
to the dissipative linear Boltzmann equation with hard--spheres collision
kernel describing inelastic interactions of a gas particles with a fixed
background. The equilibrium state is a universal Maxwellian distribution
function with the same velocity as field particles and with a non--zero
temperature lower than the background one, which depends on the details of the
binary collision. Thanks to the H--theorem we then prove strong convergence of
the solution to the Boltzmann equation towards the equilibrium.Comment: 17 pages, submitted to Journal of Statistical Physic
Effects of dietary lipids on renal function of aged rats
Normal aging is accompanied by renal functional and morphological deterioration and dietetic manipulation has been used to delay this age-related decline. We examined the effects of chronic administration of diets containing 5% lipid-enriched diet (LD, w/w) on renal function of rats at different ages. Three types of LD were tested: canola oil, fish oil and butter. Mean systemic tail-cuff blood pressure and glycemia remained within the normal range whatever the age and the diet of the animals. Proteinuria began to rise from the 8th month in the groups ingesting LD, while in the control group it increased significantly (above 10 mg/24 h) only after the 10th month. With age, a significant and progressive decline in glomerular filtration rate (GFR) and renal plasma flow was observed in the LD groups but after 6 months of lipid supplementation, the decline in these parameters was more marked in the butter and fish oil groups. By the 18th month, the lowest GFR level was observed in the group ingesting the butter diet (2.93 ± 0.22 vs 5.01 ± 0.21 ml min-1 kg-1 in control, P<0.05). Net acid excretion, evaluated in 9- and 18-month-old rats, was stimulated in the fish oil group when compared both to control and to the other two LD groups. These results suggest that even low levels of LD in a chronic nutritional regimen can modify the age-related changes in renal function and that the impact of different types of lipid-supplemented diets on renal function depends on the kind of lipid present in the diet.Universidade Federal de São Paulo (UNIFESP) Escola Paulista de Medicina Disciplina de Fisiologia Renal e TermometabologiaUNIFESP, EPM, Disciplina de Fisiologia Renal e TermometabologiaSciEL
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