3,803 research outputs found
Do columnar defects produce bulk pinning?
From magneto-optical imaging performed on heavy-ion irradiated YBaCuO single
crystals, it is found that at fields and temperatures where strong single
vortex pinning by individual irradiation-induced amorphous columnar defects is
to be expected, vortex motion is limited by the nucleation of vortex kinks at
the specimen surface rather than by half-loop nucleation in the bulk. In the
material bulk, vortex motion occurs through (easy) kink sliding. Depinning in
the bulk determines the screening current only at fields comparable to or
larger than the matching field, at which the majority of moving vortices is not
trapped by an ion track.Comment: 5 pages, 5 figures, submitted to Physical Review Letter
Thermal denaturation of fluctuating finite DNA chains: the role of bending rigidity in bubble nucleation
Statistical DNA models available in the literature are often effective models
where the base-pair state only (unbroken or broken) is considered. Because of a
decrease by a factor of 30 of the effective bending rigidity of a sequence of
broken bonds, or bubble, compared to the double stranded state, the inclusion
of the molecular conformational degrees of freedom in a more general mesoscopic
model is needed. In this paper we do so by presenting a 1D Ising model, which
describes the internal base pair states, coupled to a discrete worm like chain
model describing the chain configurations [J. Palmeri, M. Manghi, and N.
Destainville, Phys. Rev. Lett. 99, 088103 (2007)]. This coupled model is
exactly solved using a transfer matrix technique that presents an analogy with
the path integral treatment of a quantum two-state diatomic molecule. When the
chain fluctuations are integrated out, the denaturation transition temperature
and width emerge naturally as an explicit function of the model parameters of a
well defined Hamiltonian, revealing that the transition is driven by the
difference in bending (entropy dominated) free energy between bubble and
double-stranded segments. The calculated melting curve (fraction of open base
pairs) is in good agreement with the experimental melting profile of
polydA-polydT. The predicted variation of the mean-square-radius as a function
of temperature leads to a coherent novel explanation for the experimentally
observed thermal viscosity transition. Finally, the influence of the DNA strand
length is studied in detail, underlining the importance of finite size effects,
even for DNA made of several thousand base pairs.Comment: Latex, 28 pages pdf, 9 figure
Dynamics of Circumstellar Disks II: Heating and Cooling
We present a series of 2-d () hydrodynamic simulations of marginally
self gravitating disks around protostars using an SPH code. We implement simple
dynamical heating and we cool each location as a black body, using a
photosphere temperature obtained from the local vertical structure. We
synthesize SEDs from our simulations and compare them to fiducial SEDs derived
from observed systems. These simulations produce less distinct spiral structure
than isothermally evolved systems, especially in the inner third of the disk.
Pattern are similar further from the star but do not collapse into condensed
objects. The photosphere temperature is well fit to a power law in radius with
index , which is very steep. Far from the star, internal heating
( work and shocks) are not responsible for generating a large fraction of
the thermal energy contained in the disk matter. Gravitational torques
responsible for such shocks cannot transport mass and angular momentum
efficiently in the outer disk. Within 5--10 AU of the star, rapid break
up and reformation of spiral structure causes shocks, which provide sufficient
dissipation to power a larger fraction of the near IR energy output. The
spatial and size distribution of grains can have marked consequences on the
observed near IR SED and can lead to increased emission and variability on
year time scales. When grains are vaporized they do not reform
into a size distribution similar to that from which most opacity calculations
are based. With rapid grain reformation into the original size distribution,
the disk does not emit near infrared photons. With a plausible modification to
the opacity, it contributes much more.Comment: Accepted by ApJ, 60pg incl 24 figure
The Effect of Splayed Pins on Vortex Creep and Critical Currents
We study the effects of splayed columnar pins on the vortex motion using
realistic London Langevin simulations. At low currents vortex creep is strongly
suppressed, whereas the critical current j_c is enhanced only moderately.
Splaying the pins generates an increasing energy barrier against vortex
hopping, and leads to the forced entanglement of vortices, both of which
suppress creep efficiently. On the other hand splaying enhances kink nucleation
and introduces intersecting pins, which cut off the energy barriers. Thus the
j_c enhancement is strongly parameter sensitive. We also characterize the angle
dependence of j_c, and the effect of different splaying geometries.Comment: 4 figure
The Effect of Clean Water Facilities and Household Food Sanitation Hygiene on Stunting in Toddlers
Stunting is a linear growth disorder of a child's body that becomes short or short based on height for age with a Z-score threshold of < -2 standard deviations. Multi-dimensional factors, including environmental factors, cause stunting. Environmental factors that cause stunting are the mother's personal hygiene, sanitation, clean water and drinking water sources. This study aimed to determine the effect of clean water sanitation facilities and household food sanitation hygiene on stunting in toddlers. Observational study with a case-control design in children aged 0-59 months in Silahisabung District, Dairi Regency. The population used in this research is 453 toddlers aged 0-59 months. Case sampling technique using total sampling. All stunting toddlers were taken as cases of 78 toddlers and 78 as controls. Using weight scales and body length measuring instruments, research data was collected using questionnaires and tools to determine the nutritional status of babies under two years old. Data processing and analysis included univariate and bivariate using the chi-square test. The results showed that there were stunted toddlers, namely 61.5% did not have access to water facilities that met the requirements, and 44.9% of toddlers who suffered from stunting were in the age range of 21-40 months. Bivariate analysis using the chi-square test showed an effect of clean water sanitation (p=0.002, OR=2.764) and household food sanitation hygiene (p=0.004, OR=2.562) on the incidence of stunting in toddlers. Management of stunting events requires good coordination and collaboration between health workers, the government and the community in reducing risk factors. Personal hygiene will be further improved in preparing and processing food by practising the principles of food sanitation hygiene.Keywords: Food Hygiene, Sanitation, Stunting, Toddler
Ab initio Calculations of Multilayer Relaxations of Stepped Cu Surfaces
We present trends in the multilayer relaxations of several vicinals of
Cu(100) and Cu(111) of varying terrace widths and geometry. The electronic
structure calculations are based on density functional theory in the local
density approximation with norm-conserving, non-local pseudopotentials in the
mixed basis representation. While relaxations continue for several layers, the
major effect concentrates near the step and corner atoms. On all surfaces the
step atoms contract inwards, in agreement with experimental findings.
Additionally, the corner atoms move outwards and the atoms in the adjacent
chain undergo large inward relaxation. Correspondingly, the largest contraction
(4%) is in the bond length between the step atom and its bulk nearest neighbor
(BNN), while that between the corner atom and BNN is somewhat enlarged. The
surface atoms also display changes in registry of upto 1.5%. Our results are in
general in good agreement with LEED data including the controversial case of
Cu(511). Subtle differences are found with results obtained from semi-empirical
potentials.Comment: 21 pages and 3 figure
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