2,029 research outputs found
Long-Ranged Orientational Order in Dipolar Fluids
Recently Groh and Dietrich claimed the thermodynamic state of a dipolar fluid
depends on the shape of the fluid's container. For example, a homogeneous fluid
in a short fat container would phase separate when transferred to a tall skinny
container of identical volume and temperature. Their calculation thus lacks a
thermodynamic limit. We show that removal of demagnetizing fields restores the
true, shape independent, thermodynamic limit. As a consequence, spontaneously
magnetized liquids display inhomogeneous magnetization textures.Comment: 3 pages, LaTex, no figures. Submitted as comment to PRL, May 199
Analysis of electroencephalograms in Alzheimer's disease patients with multiscale entropy
The aim of this study was to analyse the electroencephalogram (EEG) background activity of Alzheimer’s disease (AD) patients using the Multiscale Entropy (MSE). The MSE is a recently developed method that quantifies the regularity of a signal on different time scales. These time scales are inspected by means of several coarse-grained sequences formed from the analysed signals. We recorded the EEGs from 19 scalp electrodes in 11 AD patients and 11 age-matched controls and estimated the MSE profile for each epoch of the EEG recordings. The shape of the MSE profiles reveals the EEG complexity, and it suggests that the EEG contains information in deeper scales than the smallest one. Moreover, the results showed that the EEG background activity is less complex in AD patients than control subjects. We found significant difference
Technical Advice and Support for the Joint Integrated Non-Intrusive Inspection (JINII) Program Task 2.2 Transmission Digital Radiography (DR)
The Cargo Advanced Automated Radiography System (CAARS) program aims to utilize advanced radiographic systems to detect radiological and nuclear threats. Validation of initial design and testing concepts is a precondition for prototype system development and large-scale deployment. As expected, Depleted Uranium (DU) is a valid surrogate for Special Nuclear Materials (SNM) in CAARS Advanced Technology Demonstration (ATD) performance field-tests of transmission radiography systems. Dual-energy transmission measurements of DU are nearly identical to SNM, and are distinct from lower Z materials, provided the samples are matched to equal areal density. Results from an alternative method, using samples of equal thickness, showed sample discrimination by material density, rather than by atomic number (Z). The transmission measurements of DU and SNM were made with equipment that is nearly identical to current field systems. X-ray source beams at endpoint energies of 5.4 MeV and 9.6 MeV were used to measure transmission through the selected sample materials. The ratio of the x-ray linear attenuation coefficient times length ({micro}L) at 5.4 MeV, to {micro}L at 9.6 MeV is a metric for atomic number based discrimination of materials. The measured ratios were compared with computed values based on LLNL photon cross section data and LLNL developed models of x-ray detector characteristics. Measured ratios for DU differed from HEU by an average of 0.25%, and from WGPu by 0.08%, which is within the noise level of 0.4 to 0.5%. For comparison, measured ratios for Sn differed from HEU by 3.2%, and from WGPu by 3.6%, well beyond the measurement noise. Measured ratios for W differed from HEU by 0.01%, and from WGPu by 0.32%. The measured ratio values presented in Table 1 demonstrate the feasibility of using a threshold ratio to discriminate low-Z (Z < 72) from high-Z (Z {ge} 72) materials (as defined by CAARS specification). In the case of our test system, a threshold ratio of 1.08 would be suitable based on the measured results
Universal reduction of pressure between charged surfaces by long-wavelength surface charge modulation
We predict theoretically that long-wavelength surface charge modulations
universally reduce the pressure between the charged surfaces with counterions
compared with the case of uniformly charged surfaces with the same average
surface charge density. The physical origin of this effect is the fact that
surface charge modulations always lead to enhanced counterion localization near
the surfaces, and hence, fewer charges at the midplane. We confirm the last
prediction with Monte Carlo simulations.Comment: 8 pages 1 figure, Europhys. Lett., in pres
Charge-Fluctuation-Induced Non-analytic Bending Rigidity
In this Letter, we consider a neutral system of mobile positive and negative
charges confined on the surface of curved films. This may be an appropriate
model for: i) a highly charged membrane whose counterions are confined to a
sheath near its surface; ii) a membrane composed of an equimolar mixture of
anionic and cationic surfactants in aqueous solution. We find that the charge
fluctuations contribute a non-analytic term to the bending rigidity that varies
logarithmically with the radius of curvature. This may lead to spontaneous
vesicle formation, which is indeed observed in similar systems.Comment: Revtex, 9 pages, no figures, submitted to PR
Prognostic factors for chronic headache: A systematic review
OBJECTIVE: To identify predictors of prognosis and trial outcomes in prospective studies of people with chronic headache. METHODS: This was a systematic review of published literature in peer-reviewed journals. We included (1) randomized controlled trials (RCTs) of interventions for chronic headache that reported subgroup analyses and (2) prospective cohort studies, published in English, since 1980. Participants included adults with chronic headache (including chronic headache, chronic migraine, and chronic tension-type headache with or without medication overuse headache). We searched key databases using free text and MeSH terms. Two reviewers independently extracted data and assessed the methodologic quality of studies and overall quality of evidence identified using appropriate published checklists. RESULTS: We identified 16,556 titles, removed 663 duplicates, and reviewed 199 articles, of which 27 were included in the review-17 prospective cohorts and 10 RCTs with subgroup analyses reported. There was moderate-quality evidence indicating that depression, anxiety, poor sleep and stress, medication overuse, and poor self-efficacy for managing headaches are potential prognostic factors for poor prognosis and unfavorable outcomes from preventive treatment in chronic headache. There was inconclusive evidence about treatment expectations, age, age at onset, body mass index, employment, and several headache features. CONCLUSIONS: This review identified several potential predictors of poor prognosis and worse outcome postinterventions in people with chronic headache. The majority of these are modifiable. The findings also highlight the need for more longitudinal high-quality research of prognostic factors in chronic headache
Scaling Behaviour and Complexity of the Portevin-Le Chatelier Effect
The plastic deformation of dilute alloys is often accompanied by plastic
instabilities due to dynamic strain aging and dislocation interaction. The
repeated breakaway of dislocations from and their recapture by solute atoms
leads to stress serrations and localized strain in the strain controlled
tensile tests, known as the Portevin-Le Chatelier (PLC) effect. In this present
work, we analyse the stress time series data of the observed PLC effect in the
constant strain rate tensile tests on Al-2.5%Mg alloy for a wide range of
strain rates at room temperature. The scaling behaviour of the PLC effect was
studied using two complementary scaling analysis methods: the finite variance
scaling method and the diffusion entropy analysis. From these analyses we could
establish that in the entire span of strain rates, PLC effect showed Levy walk
property. Moreover, the multiscale entropy analysis is carried out on the
stress time series data observed during the PLC effect to quantify the
complexity of the distinct spatiotemporal dynamical regimes. It is shown that
for the static type C band, the entropy is very low for all the scales compared
to the hopping type B and the propagating type A bands. The results are
interpreted considering the time and length scales relevant to the effect.Comment: 35 pages, 6 figure
Screening by symmetry of long-range hydrodynamic interactions of polymers confined in sheets
Hydrodynamic forces may significantly affect the motion of polymers. In
sheet-like cavities, such as the cell's cytoplasm and microfluidic channels,
the hydrodynamic forces are long-range. It is therefore expected that that
hydrodynamic interactions will dominate the motion of polymers in sheets and
will be manifested by Zimm-like scaling. Quite the opposite, we note here that
although the hydrodynamic forces are long-range their overall effect on the
motion of polymers vanishes due to the symmetry of the two-dimensional flow. As
a result, the predicted scaling of experimental observables such as the
diffusion coefficient or the rotational diffusion time is Rouse-like, in accord
with recent experiments. The effective screening validates the use of the
non-interacting blobs picture for polymers confined in a sheet.Comment: http://www.weizmann.ac.il/complex/tlusty/papers/Macromolecules2006.pdf
http://pubs.acs.org/doi/abs/10.1021/ma060251
On the signature of tensile blobs in the scattering function of a stretched polymer
We present Monte Carlo data for a linear chain with excluded volume subjected
to a uniform stretching. Simulation of long chains (up to 6000 beads) at high
stretching allows us to observe the signature of tensile blobs as a crossover
in the scaling behavior of the chain scattering function for wave vectors
perpendicular to stretching. These results and corresponding ones in the
stretching direction allow us to verify for the first time Pincus prediction on
scaling inside blobs. Outside blobs, the scattering function is well described
by the Debye function for a stretched ideal chain.Comment: 4 pages, 4 figures, to appear in Physical Review Letter
The field theoretic derivation of the contact value theorem in planar geometries and its modification by the Casimir effect
The contact value theorem for Coulomb gases in planar or film-like geometries
is derived using a Hamiltonian field theoretic representation of the system.
The case where the film is enclosed by a material of different dielectric
constant to that of the film is shown to contain an additional Casimir-like
term which is generated by fluctuations of the electric potential about its
mean-field value.Comment: Link between Sine-Gordon and Coulomb gas pressures via subtraction of
self interaction terms included. Discussion of results within Debye-Huckel
approximation included. Added reference
- …