2,394 research outputs found
Scalable coexistence of eMBB, URLLC and mMTC enabled by non-orthogonal multiple access and network slicing
Abstract. The 5G systems feature three use cases: enhanced Mobile BroadBand (eMBB), massive Machine-Type Communications (mMTC) and Ultra-Reliable and Low-Latency Communications (URLLC). The diverse requirements of the corresponding services in terms of achievable data-rate, number of connected devices, latency and reliability can lead to sub-optimal use of the 5G resources, thus network slicing emerges as a promising alternative that customizes slices of the network specifically designed to meet specific requirements. By employing network slicing, the radio resources can be shared via orthogonal and non-orthogonal schemes. Motivated by the Industrial Internet of Things (IIoT) paradigm where a large number of sensors may require connectivity with stringent requirements of latency and reliability, we propose and evaluate the joint use of network slicing and Non-Orthogonal Multiple Access (NOMA) with Successive Interference Cancellation (SIC) in two different uplink scenarios. In the first scenario, eMBB coexists with URLLC in the same Radio Access Network (RAN) and, in order to improve the number of concurrent URLLC connections to the same base station (BS), they transmit simultaneously and across multiple frequency channels. In the second scenario, eMBB coexists with mMTC and, to provide connectivity to a massive number of devices, the BS has multiple receive antennas. In both cases, we set the reliability requirements for the services and compare the performance of both orthogonal and non-orthogonal network slicing schemes in terms of maximum achievable data rates and connected users. Our results show that, even with overlapping transmissions from multiple devices, network slicing, NOMA and SIC techniques allow us simultaneously satisfy all the heterogeneous requirements of the 5G services
M-sequence geomagnetic polarity time scale (MHTC12) that steadies global spreading rates and incorporates astrochronology constraints
Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): B06104, doi:10.1029/2012JB009260.Geomagnetic polarity time scales (GPTSs) have been constructed by interpolating between dated marine magnetic anomalies assuming uniformly varying spreading rates. A strategy to obtain an optimal GPTS is to minimize spreading rate fluctuations in many ridge systems; however, this has been possible only for a few spreading centers. We describe here a Monte Carlo sampling method that overcomes this limitation and improves GPTS accuracy by incorporating information on polarity chron durations estimated from astrochronology. The sampling generates a large ensemble of GPTSs that simultaneously agree with radiometric age constraints, minimize the global variation in spreading rates, and fit polarity chron durations estimated by astrochronology. A key feature is the inclusion and propagation of data uncertainties, which weigh how each piece of information affects the resulting time scale. The average of the sampled ensemble gives a reference GPTS, and the variance of the ensemble measures the time scale uncertainty. We apply the method to construct MHTC12, an improved version of the M-sequence GPTS (Late Jurassic-Early Cretaceous, ~160–120 Ma). This GPTS minimizes the variation in spreading rates in a global data set of magnetic lineations from the Western Pacific, North Atlantic, and Indian Ocean NW of Australia, and it also accounts for the duration of five polarity chrons established from astrochronology (CM0r through CM3r). This GPTS can be updated by repeating the Monte Carlo sampling with additional data that may become available in the future.A.M. and J.H. were supported by NSF grant
OCE 09–26306, M.T. was supported by a Woods Hole Oceanographic
Institution postdoctoral scholarship, and J.E.T.C. was supported by NSF
grant OCE 09–60999.2012-12-3
The Nucleosynthetic Imprint of 15-40 Solar Mass Primordial Supernovae on Metal-Poor Stars
The inclusion of rotationally-induced mixing in stellar evolution can alter
the structure and composition of presupernova stars. We survey the effects of
progenitor rotation on nucleosynthetic yields in Population III and II
supernovae using the new adaptive mesh refinement (AMR) code CASTRO. We examine
spherical explosions in 15, 25 and 40 solar mass stars at Z = 0 and 10^-4 solar
metallicity with three explosion energies and two rotation rates. Rotation in
the Z = 0 models resulted in primary nitrogen production and a stronger
hydrogen burning shell which led all models to die as red supergiants. On the
other hand, the Z=10^-4 solar metallicity models that included rotation ended
their lives as compact blue stars. Because of their extended structure, the
hydrodynamics favors more mixing and less fallback in the metal free stars than
the Z = 10^-4 models. As expected, higher energy explosions produce more
enrichment and less fallback than do lower energy explosions, and less massive
stars produce more enrichment and leave behind smaller remnants than do more
massive stars. We compare our nucleosynthetic yields to the chemical abundances
in the three most iron-poor stars yet found and reproduce the abundance pattern
of one, HE 0557-4840, with a zero metallicity 15 solar mass, 2.4 x 10^51 erg
supernova. A Salpeter IMF averaged integration of our yields for Z=0 models
with explosion energies of 2.4x10^51 ergs or less is in good agreement with the
abundances observed in larger samples of extremely metal-poor stars, provided
15 solar mass stars are included. Since the abundance patterns of extremely
metal-poor stars likely arise from a representative sample of progenitors, our
yields suggest that low-mass supernovae contributed the bulk of the metals to
the early universe.Comment: 16 pages, 11 figures; submitted to Ap
Picosecond strain dynamics in GeSbTe monitored by time-resolved x-ray diffraction
Coherent phonons (CP) generated by laser pulses on the femtosecond scale have
been proposed as a means to achieve ultrafast, non-thermal switching in
phase-change materials such as GeSbTe(GST). Here we use
ultrafast optical pump pulses to induce coherent acoustic phonons and
stroboscopically measure the corresponding lattice distortions in GST using 100
ps x-ray pulses from the ESRF storage ring. A linear-chain model provides a
good description of the observed changes in the diffraction signal, however,
the magnitudes of the measured shifts are too large to be explained by thermal
effects alone implying the presence of transient non-equilibrium electron
heating in addition to temperature driven expansion. The information on the
movement of atoms during the excitation process can lead to greater insight
into the possibilities of using CP-induced phase-transitions in GST.Comment: 7 pages, 4 figures, Phys. Rev. B, in pres
Dynamical Susceptibility in KDP-type Crysals above and below Tc II
The path probability method (PPM) in the tetrahedron-cactus approximation is
applied to the Slater-Takagi model with dipole-dipole interaction for
KH2PO4-type hydrogen-bonded ferroelectric crystals in order to derive a small
dip structure in the real part of dynamical susceptibility observed at the
transition temperature Tc. The dip structure can be ascribed to finite
relaxation times of electric dipole moments responsible for the first order
transition with contrast to the critical slowing down in the second order
transition. The light scattering intensity which is related to the imaginary
part of dynamical susceptibility is also calculated above and below the
transition temperature and the obtained central peak structure is consistent
with polarization fluctuation modes in Raman scattering experiments.Comment: 8 pages, 11 figure
SN 2006aj Associated with XRF 060218 At Late Phases: Nucleosynthesis-Signature of A Neutron Star-Driven Explosion
Optical spectroscopy and photometry of SN 2006aj have been performed with the
Subaru telescope at t > 200 days after GRB060218, the X-ray Flash with which it
was associated. Strong nebular emission-lines with an expansion velocity of v ~
7,300 km/s were detected. The peaked but relatively broad [OI]6300,6363
suggests the existence of ~ 2 Msun of materials in which ~1.3 Msun is oxygen.
The core might be produced by a mildly asymmetric explosion. The spectra are
unique among SNe Ic in (1) the absence of [CaII]7291,7324 emission, and (2) a
strong emission feature at ~ 7400A, which requires ~ 0.05 Msun of
newly-synthesized 58Ni. Such a large amount of stable neutron-rich Ni strongly
indicates the formation of a neutron star. The progenitor and the explosion
energy are constrained to 18 Msun < Mms < 22 Msun and E ~ (1 - 3) 10^{51} erg,
respectively.Comment: Accepted for Publication in the Astrophysical Journal Letters (2007,
ApJ, 658, L5). 8 pages, including 1 table and 3 figures. Typos correcte
Shock Breakout in Type II Plateau Supernovae: Prospects for High Redshift Supernova Surveys
Shock breakout is the brightest radiative phenomenon in a supernova (SN) but
is difficult to be observed owing to the short duration and X-ray/ultraviolet
(UV)-peaked spectra. After the first observation from the rising phase reported
in 2008, its observability at high redshift is attracting enormous attention.
We perform multigroup radiation hydrodynamics calculations of explosions for
evolutionary presupernova models with various main-sequence masses , metallicities , and explosion energies . We present multicolor
light curves of shock breakout in Type II plateau SNe, being the most frequent
core-collapse SNe, and predict apparent multicolor light curves of shock
breakout at various redshifts . We derive the observable SN rate and
reachable redshift as functions of filter and limiting magnitude by taking into account an initial mass function, cosmic star formation
history, intergalactic absorption, and host galaxy extinction. We propose a
realistic survey strategy optimized for shock breakout. For example, the
-band observable SN rate for mag is 3.3 SNe
degree day and a half of them locates at . It is clear
that the shock breakout is a beneficial clue to probe high- core-collapse
SNe. We also establish ways to identify shock breakout and constrain SN
properties from the observations of shock breakout, brightness, time scale, and
color. We emphasize that the multicolor observations in blue optical bands with
hour intervals, preferably over continuous nights, are essential
to efficiently detect, identify, and interpret shock breakout.Comment: 26 pages, 23 figures. Accepted for publication in the Astrophysical
Journal Supplement Serie
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