665 research outputs found
Magnetic and Transport Properties of Fe-Ag granular multilayers
Results of magnetization, magnetotransport and Mossbauer spectroscopy
measurements of sequentially evaporated Fe-Ag granular composites are
presented. The strong magnetic scattering of the conduction electrons is
reflected in the sublinear temperature dependence of the resistance and in the
large negative magnetoresistance. The simultaneous analysis of the magnetic
properties and the transport behavior suggests a bimodal grain size
distribution. A detailed quantitative description of the unusual features
observed in the transport properties is given
Absence of molecular mobility on nano-second time scales in amorphous ice phases
High-resolution neutron backscattering techniques are exploited to study the
elastic and quasi-elastic response of the high-density amorphous (HDA), the
low-density amorphous (LDA) and the crystalline ice Ic upon temperature
changes. Within the temperature ranges of their structural stability (HDA at T
> 80 K, LDA at T > 135 K, ice Ic at T < 200 K) the Debye-Waller factors and
mean-square displacements characterise all states as harmonic solids. During
the transformations HDA->LDA (T ~ 100 K), LDA->Ic (T ~ 150K) and the supposed
glass transition with Tg ~ 135 K no relaxation processes can be detected on a
time scale t < 4 ns. It can be concluded from coherent scattering measurements
(D_2O) that LDA starts to recrystallise into ice Ic at T ~ 135 K, i.e. at the
supposed Tg. In the framework of the Debye model of harmonic solids HDA reveals
the highest Debye temperature among the studied ice phases, which is in full
agreement with the lowest Debye level in the generalised density of states
derived from time-of-flight neutron scattering experiments. The elastic results
at low T indicate the presence of an excess of modes in HDA, which do not obey
the Bose statistics
The Infrared Camera (IRC) for AKARI - Design and Imaging Performance
The Infrared Camera (IRC) is one of two focal-plane instruments on the AKARI
satellite. It is designed for wide-field deep imaging and low-resolution
spectroscopy in the near- to mid-infrared (1.8--26.5um) in the pointed
observation mode of AKARI. IRC is also operated in the survey mode to make an
all-sky survey at 9 and 18um. It comprises three channels. The NIR channel
(1.8--5.5um) employs a 512 x 412 InSb array, whereas both the MIR-S
(4.6--13.4um) and MIR-L (12.6--26.5um) channels use 256 x 256 Si:As impurity
band conduction arrays. Each of the three channels has a field-of-view of about
10' x 10' and are operated simultaneously. The NIR and MIR-S share the same
field-of-view by virtue of a beam splitter. The MIR-L observes the sky about
$25' away from the NIR/MIR-S field-of-view. IRC gives us deep insights into the
formation and evolution of galaxies, the evolution of planetary disks, the
process of star-formation, the properties of interstellar matter under various
physical conditions, and the nature and evolution of solar system objects. The
in-flight performance of IRC has been confirmed to be in agreement with the
pre-flight expectation. This paper summarizes the design and the in-flight
operation and imaging performance of IRC.Comment: Publications of the Astronomical Society of Japan, in pres
Construction of the free energy landscape by the density functional theory
On the basis of the density functional theory, we give a clear definition of
the free energy landscape. To show the usefulness of the definition, we
construct the free energy landscape for rearrangement of atoms in an FCC
crystal of hard spheres. In this description, the cooperatively rearranging
region (CRR) is clealy related to the hard spheres involved in the saddle
between two adjacent basins. A new concept of the simultaneously rearranging
region (SRR) emerges naturally as spheres defined by the difference between two
adjacent basins. We show that the SRR and the CRR can be determined explicitly
from the free energylandscape.Comment: 11 pages, 3 figures, submitted to J. Chem. Phy
The relationship between fragility, configurational entropy and the potential energy landscape of glass forming liquids
Glass is a microscopically disordered, solid form of matter that results when
a fluid is cooled or compressed in such a fashion that it does not crystallise.
Almost all types of materials are capable of glass formation -- polymers, metal
alloys, and molten salts, to name a few. Given such diversity, organising
principles which systematise data concerning glass formation are invaluable.
One such principle is the classification of glass formers according to their
fragility\cite{fragility}. Fragility measures the rapidity with which a
liquid's properties such as viscosity change as the glassy state is approached.
Although the relationship between features of the energy landscape of a glass
former, its configurational entropy and fragility have been analysed previously
(e. g.,\cite{speedyfr}), an understanding of the origins of fragility in these
features is far from being well established. Results for a model liquid, whose
fragility depends on its bulk density, are presented in this letter. Analysis
of the relationship between fragility and quantitative measures of the energy
landscape (the complicated dependence of energy on configuration) reveal that
the fragility depends on changes in the vibrational properties of individual
energy basins, in addition to the total number of such basins present, and
their spread in energy. A thermodynamic expression for fragility is derived,
which is in quantitative agreement with {\it kinetic} fragilities obtained from
the liquid's diffusivity.Comment: 8 pages, 3 figure
Analysis of 5G RAN Configuration to Support Advanced V2X Services
5G offers high flexibility at the radio, transport and core networks to support various services of critical verticals such as connected and automated driving. At the Radio Access Network (RAN), 5G defines a New Radio (NR). 5G NR utilizes different subcarrier spacing, slot durations, modulations and channel coding schemes. This flexibility offers the possibility to support automotive services with different and demanding requirements, such as Advanced Driver-Assistance System (ADAS), cooperative driving, and remote driving. Previous studies showed that 5G NR can be configured to achieve latencies below 2 ms. However, existing studies are generally restricted to scenarios with a limited number of users and unlimited bandwidth. Therefore, it is important to analyze whether 5G NR can effectively support these services as the network scales under limited spectrum allocations. This study advances the current state of the art to demonstrate that the capability of 5G NR RAN to support advanced V2X services depends on the RAN configuration (subcarrier spacing, slot duration and error protection) and network loadUMH work was supported in part by the Spanish Ministry of Science and Innovation (MCI), AEI and FEDER funds under Project TEC2017-88612-R,and the Ministry of Universities (IJC2018-036862-I), and the Generalitat Valencian
On the Scalability of the 5G RAN to Support Advanced V2X Services
Cellular networks currently support non-safety-critical Vehicle to Everything (V2X) services with relaxed latency and reliability requirements. 5G introduces novel technologies at the radio, transport and core networks that are expected to significantly reduce the latency and increase the flexibility and reliability of cellular networks. This has raised expectations on the possibility for 5G to support advanced V2X applications, including connected and automated applications such as advanced ADAS services, cooperative driving and remote driving. At the radio access network (RAN), 5G introduces the New Radio (NR) interface that incorporates flexible numerologies and new slot formats, channel coding schemes, and radio resource management processes. Previous studies have reported latency values of 5G NR below 2 ms when considering scenarios with limited users in the cell and with unlimited bandwidth. Supporting advanced V2X services using 5G requires a scalable network capable to support a larger number of users without degrading the required service level in scenarios with potentially limited spectrum. This study advances the current state of the art with the evaluation of the scalability of the 5G NR RAN. As a case study, the paper evaluates the capacity of 5G RAN to support the latency and reliability requirements of the cooperative lane change use case as the network load varies. The results show that the capacity of the 5G RAN to support advanced V2X services depends on the system configuration, network load and service requirements. These results call for a careful design, configuration and planning of 5G networks to support V2X services.UMH work was supported in part by the Spanish Ministry of Science and Innovation (MCI), AEI and FEDER funds under Project TEC2017-88612-R, and the Ministry of Universities (IJC2018-036862-I)
Controllability on infinite-dimensional manifolds
Following the unified approach of A. Kriegl and P.W. Michor (1997) for a
treatment of global analysis on a class of locally convex spaces known as
convenient, we give a generalization of Rashevsky-Chow's theorem for control
systems in regular connected manifolds modelled on convenient
(infinite-dimensional) locally convex spaces which are not necessarily
normable.Comment: 19 pages, 1 figur
Harmonic Vibrational Excitations in Disordered Solids and the "Boson Peak"
We consider a system of coupled classical harmonic oscillators with spatially
fluctuating nearest-neighbor force constants on a simple cubic lattice. The
model is solved both by numerically diagonalizing the Hamiltonian and by
applying the single-bond coherent potential approximation. The results for the
density of states are in excellent agreement with each other. As
the degree of disorder is increased the system becomes unstable due to the
presence of negative force constants. If the system is near the borderline of
stability a low-frequency peak appears in the reduced density of states
as a precursor of the instability. We argue that this peak
is the analogon of the "boson peak", observed in structural glasses. By means
of the level distance statistics we show that the peak is not associated with
localized states
Theoretical Evaluation of the Reaction Rates for 26Al(n,p)26Mg and 26Al(n,a)23Na
The reactions that destroy 26Al in massive stars have significance in a
number of astrophysical contexts. We evaluate the reaction rates of
26Al(n,p)26Mg and 26Al(n,a)23Na using cross sections obtained from the codes
EMPIRE and TALYS. These have been compared to the published rates obtained from
the non-smoker code and to some experimental data. We show that the results
obtained from EMPIRE and TALYS are comparable to those from non-smoker. We also
show how the theoretical results vary with respect to changes in the input
parameters. Finally, we present recommended rates for these reactions using the
available experimental data and our new theoretical results
- …