1,012 research outputs found
A Lagrangian approach to modeling heat flux driven close-contact melting
Close-contact melting refers to the process of a heat source melting its way
into a phase-change material. Of special interest is the close-contact melting
velocity, or more specifically the relative velocity between the heat source
and the phase-change material. In this work, we present a novel numerical
approach to simulate quasi-steady, heat flux driven close-contact melting. It
extends existing approaches found in the literature, and, for the first time,
allows to study the impact of a spatially varying heat flux distribution. We
will start by deriving the governing equations in a Lagrangian reference frame
fixed to the heat source. Exploiting the narrowness of the melt film enables us
to reduce the momentum balance to the Reynolds equation, which is coupled to
the energy balance via the velocity field. We particularize our derivation for
two simple, yet technically relevant geometries, namely a 3d circular disc and
a 2d planar heat source. An iterative solution procedure for the coupled system
is described in detail and discussed on the basis of a convergence study.
Furthermore, we present an extension to allow for rotational melting modes.
Various test cases demonstrate the proficiency of our method. In particular, we
will utilize the method to assess the efficiency of the close-contact melting
process and to quantify the model error introduced if convective losses are
neglected. Finally, we will draw conclusions and present an outlook to future
work
Electron spin relaxation in paramagnetic Ga(Mn)As quantum wells
Electron spin relaxation in paramagnetic Ga(Mn)As quantum wells is studied
via the fully microscopic kinetic spin Bloch equation approach where all the
scatterings, such as the electron-impurity, electron-phonon, electron-electron
Coulomb, electron-hole Coulomb, electron-hole exchange (the Bir-Aronov-Pikus
mechanism) and the - exchange scatterings, are explicitly included. The
Elliot-Yafet mechanism is also incorporated. From this approach, we study the
spin relaxation in both -type and -type Ga(Mn)As quantum wells. For
-type Ga(Mn)As quantum wells where most Mn ions take the interstitial
positions, we find that the spin relaxation is always dominated by the DP
mechanism in metallic region. Interestingly, the Mn concentration dependence of
the spin relaxation time is nonmonotonic and exhibits a peak. This behavior is
because that the momentum scattering and the inhomogeneous broadening have
different density dependences in the non-degenerate and degenerate regimes. For
-type Ga(Mn)As quantum wells, we find that Mn concentration dependence of
the spin relaxation time is also nonmonotonic and shows a peak. Differently,
this behavior is because that the - exchange scattering (or the
Bir-Aronov-Pikus) mechanism dominates the spin relaxation in the high Mn
concentration regime at low (or high) temperature, whereas the DP mechanism
determines the spin relaxation in the low Mn concentration regime. The
Elliot-Yafet mechanism also contributes the spin relaxation at intermediate
temperature. The spin relaxation time due to the DP mechanism increases with Mn
concentration due to motional narrowing, whereas those due to the spin-flip
mechanisms decrease with Mn concentration, which thus leads to the formation of
the peak.... (The remaining is omitted due to the space limit)Comment: 12 pages, 8 figures, Phys. Rev. B 79, 2009, in pres
Scanning Raman spectroscopy of graphene antidot lattices: Evidence for systematic p-type doping
We have investigated antidot lattices, which were prepared on exfoliated
graphene single layers via electron-beam lithography and ion etching, by means
of scanning Raman spectroscopy. The peak positions, peak widths and intensities
of the characteristic phonon modes of the carbon lattice have been studied
systematically in a series of samples. In the patterned samples, we found a
systematic stiffening of the G band mode, accompanied by a line narrowing,
while the 2D mode energies are found to be linearly correlated with the G mode
energies. We interpret this as evidence for p-type doping of the nanostructured
graphene
Identification and characterisation of enteroaggregative Escherichia coli subtypes associated with human disease
Enteroaggregative E. coli (EAEC) are a major cause of diarrhoea worldwide. Due to their heterogeneity and carriage in healthy individuals, identification of diagnostic virulence markers for pathogenic strains has been difficult. In this study, we have determined phenotypic and genotypic differences between EAEC strains of sequence types (STs) epidemiologically associated with asymptomatic carriage (ST31) and diarrhoeal disease (ST40). ST40 strains demonstrated significantly enhanced intestinal adherence, biofilm formation, and pro-inflammatory interleukin-8 secretion compared with ST31 isolates. This was independent of whether strains were derived from diarrhoea patients or healthy controls. Whole genome sequencing revealed differences in putative virulence genes encoding aggregative adherence fimbriae, E. coli common pilus, flagellin and EAEC heat-stable enterotoxin 1. Our results indicate that ST40 strains have a higher intrinsic potential of human pathogenesis due to a specific combination of virulence-related factors which promote host cell colonization and inflammation. These findings may contribute to the development of genotypic and/or phenotypic markers for EAEC strains of high virulence
Hepatic Artery Infusion Chemotherapy
Hepatic artery chemotherapy was given to 36 patients, using totally implantable devices consisting of a port
and external pump. Twenty-seven patients had inoperable liver metastases of colorectal origin. The infusion
system was inserted by laparotomy into the hepatic artery via the gastroduodenal artery. There was no
operative mortality. Thirteen infusion systems could not be used for chemotherapy due to dislodgement,
early death and lack of follow-up. FUdR was infused every two weeks. There were minor local
complications like thrombosis of the system and dislodgement of the port. Toxic effects could be managed
by reducing the dose. Response to chemotherapy was evaluated by survival, clinical condition, CEA,
ultrasound and CT six months after onset of arterial chemotherapy. Ten/twenty-three patients (43%)
responded to therapy, eight of them died on the average 19 months after initial chemotherapy. Six patients
were non-responders, seven had stable disease. Five/ten patients developed extrahepatic metastases. Mean
survival time was 13.1 months, mean interval until relapse 10.6 months
Low-temperature photocarrier dynamics in monolayer MoS2
The band structure of MoS strongly depends on the number of layers, and a
transition from indirect to direct-gap semiconductor has been observed recently
for a single layer of MoS. Single-layer MoS therefore becomes an
efficient emitter of photoluminescence even at room temperature. Here, we
report on scanning Raman and on temperature-dependent, as well as time-resolved
photoluminescence measurements on single-layer MoS flakes prepared by
exfoliation. We observe the emergence of two distinct photoluminescence peaks
at low temperatures. The photocarrier recombination at low temperatures occurs
on the few-picosecond timescale, but with increasing temperatures, a
biexponential photoluminescence decay with a longer-lived component is
observed.Comment: 3 pages, 4 figure
Statics and Dynamics of the Wormlike Bundle Model
Bundles of filamentous polymers are primary structural components of a broad
range of cytoskeletal structures, and their mechanical properties play key
roles in cellular functions ranging from locomotion to mechanotransduction and
fertilization. We give a detailed derivation of a wormlike bundle model as a
generic description for the statics and dynamics of polymer bundles consisting
of semiflexible polymers interconnected by crosslinking agents. The elastic
degrees of freedom include bending as well as twist deformations of the
filaments and shear deformation of the crosslinks. We show that a competition
between the elastic properties of the filaments and those of the crosslinks
leads to renormalized effective bend and twist rigidities that become
mode-number dependent. The strength and character of this dependence is found
to vary with bundle architecture, such as the arrangement of filaments in the
cross section and pretwist. We discuss two paradigmatic cases of bundle
architecture, a uniform arrangement of filaments as found in F-actin bundles
and a shell-like architecture as characteristic for microtubules. Each
architecture is found to have its own universal ratio of maximal to minimal
bending rigidity, independent of the specific type of crosslink induced
filament coupling; our predictions are in reasonable agreement with available
experimental data for microtubules. Moreover, we analyze the predictions of the
wormlike bundle model for experimental observables such as the tangent-tangent
correlation function and dynamic response and correlation functions. Finally,
we analyze the effect of pretwist (helicity) on the mechanical properties of
bundles. We predict that microtubules with different number of protofilaments
should have distinct variations in their effective bending rigidity
- …