21,064 research outputs found
Quantum criticality in spin chains with non-ohmic dissipation
We investigate the critical behavior of a spin chain coupled to bosonic baths
characterized by a spectral density proportional to , with .
Varying changes the effective dimension of the
system, where is the dynamical critical exponent and the number of spatial
dimensions is set to one. We consider two extreme cases of clock models,
namely Ising-like and U(1)-symmetric ones, and find the critical exponents
using Monte Carlo methods. The dynamical critical exponent and the anomalous
scaling dimension are independent of the order parameter symmetry for
all values of . The dynamical critical exponent varies continuously from for to for , and the anomalous scaling dimension
evolves correspondingly from to . The latter
exponent values are readily understood from the effective dimensionality of the
system being for , while for the anomalous
dimension takes the well-known exact value for the 2D Ising and XY models,
since then . A noteworthy feature is, however, that
approaches unity and approaches 1/4 for values of , while naive
scaling would predict the dissipation to become irrelevant for . Instead,
we find that for for both Ising-like and U(1)
order parameter symmetry. These results lead us to conjecture that for all
site-dissipative chains, these two exponents are related by the scaling
relation . We also connect our results to
quantum criticality in nondissipative spin chains with long-range spatial
interactions.Comment: 8 pages, 6 figure
Optimising energy efficiency of non-orthogonal multiple access for wireless backhaul in heterogeneous cloud radio access network
This paper studies the downlink problem of a cloud-based central station (CCS) to multiple base stations (BSs) in a heterogeneous cellular network sharing the same time and frequency resources. We adopt non-orthogonal multiple access (NOMA) and propose power allocation for the wireless downlink in the heterogeneous cloud radio access network (HCRAN). Taking into account practical channel modelling with power consumptions at BSs of different cell types (e.g. macro-cell, micro-cell, etc.) and backhauling power, we analyse the energy efficiency (EE) of the practical HCRAN utilising NOMA. Simulation results indicate that the proposed NOMA for the HCRAN outperforms the conventional orthogonal frequency division multiple access (OFDMA) scheme in terms of providing higher EE of up to four times. Interestingly, the results reveal a fact that the EE of the NOMA approach is not always an increasing function of the number of BSs but varies as a quasiconcave function. This motivates us to further introduce an optimisation problem to find the optimal number of BSs that maximises the EE of the HCRAN. It is shown that, with a low power supply at the CCS, a double number of micro BSs can be served by HCRAN providing an improved EE of up to 1.6 times compared to the macro BSs and RRHs, while they achieve the same EE performance with high-power CCS
Hamiltonian lattice QCD at finite chemical potential
At sufficiently high temperature and density, quantum chromodynamics (QCD) is
expected to undergo a phase transition from the confined phase to the
quark-gluon plasma phase. In the Lagrangian lattice formulation the Monte Carlo
method works well for QCD at finite temperature, however, it breaks down at
finite chemical potential. We develop a Hamiltonian approach to lattice QCD at
finite chemical potential and solve it in the case of free quarks and in the
strong coupling limit. At zero temperature, we calculate the vacuum energy,
chiral condensate, quark number density and its susceptibility, as well as mass
of the pseudoscalar, vector mesons and nucleon. We find that the chiral phase
transition is of first order, and the critical chemical potential is (dynamical quark mass at ). This is consistent with
(where is the nucleon mass at ).Comment: Final version appeared in Phys. Rev.
Words are Malleable: Computing Semantic Shifts in Political and Media Discourse
Recently, researchers started to pay attention to the detection of temporal
shifts in the meaning of words. However, most (if not all) of these approaches
restricted their efforts to uncovering change over time, thus neglecting other
valuable dimensions such as social or political variability. We propose an
approach for detecting semantic shifts between different viewpoints--broadly
defined as a set of texts that share a specific metadata feature, which can be
a time-period, but also a social entity such as a political party. For each
viewpoint, we learn a semantic space in which each word is represented as a low
dimensional neural embedded vector. The challenge is to compare the meaning of
a word in one space to its meaning in another space and measure the size of the
semantic shifts. We compare the effectiveness of a measure based on optimal
transformations between the two spaces with a measure based on the similarity
of the neighbors of the word in the respective spaces. Our experiments
demonstrate that the combination of these two performs best. We show that the
semantic shifts not only occur over time, but also along different viewpoints
in a short period of time. For evaluation, we demonstrate how this approach
captures meaningful semantic shifts and can help improve other tasks such as
the contrastive viewpoint summarization and ideology detection (measured as
classification accuracy) in political texts. We also show that the two laws of
semantic change which were empirically shown to hold for temporal shifts also
hold for shifts across viewpoints. These laws state that frequent words are
less likely to shift meaning while words with many senses are more likely to do
so.Comment: In Proceedings of the 26th ACM International on Conference on
Information and Knowledge Management (CIKM2017
DPSCs from Inflamed Pulp Modulate Macrophage Function via the TNF-α/IDO Axis
Human dental pulp stem cells (DPSCs) can be isolated from inflamed pulp derived from carious teeth with symptomatic irreversible pulpitis (I-DPSCs), which possess stemness and multidifferentiation potentials similar to DPSCs from healthy pulp. Since macrophages—essential cell players of the pulpal innate immunity—can regulate pulpal inflammation and repair, the authors investigated the immunomodulatory effects of DPSCs/I-DPSCs on macrophage functions and their underlying mechanisms. Similar to DPSCs, I-DPSCs were capable of colony-forming efficiency and adipogenic and osteo/dentinogenic differentiation under in vitro induction conditions. I-DPSCs also expressed a similar phenotypic profile of mesenchymal stem cell markers, except a relatively higher level of CD146 as compared with DPSCs. Coculture of DPSCs or I-DPSCs with differentiated THP-1 cells, the human monocyte cell line, markedly suppressed tumor necrosis factor α (TNF-α) secretion in response to stimulation with lipopolysaccharides (LPS) and/or nigericin. However, unlike TNF-α, the secreted level of interleukin 1β was not affected by coculture with DPSCs or I-DPSCs. Furthermore, DPSC/I-DPSC-mediated inhibition of TNF-α secretion by macrophages was abolished by pretreatment with 1-methyl-D-tryptophan, a specific inhibitor of indoleamine-pyrrole 2,3-dioxygenase (IDO), but not by NSC-398, a specific inhibitor of COX-2, suggesting IDO as a mediator. Interestingly, IDO expression was significantly augmented in macrophages and mesenchymal stromal cells in inflamed human pulp tissues. Collectively, these findings show that I-DPSCs, similar to DPSCs, possess stem cell properties and suppress macrophage functions via the TNF-α/IDO axis, thereby providing a physiologically relevant context for their innate immunomodulatory activity in the dental pulp and their capability for pulp repair
Time-Varying Gravitomagnetism
Time-varying gravitomagnetic fields are considered within the linear
post-Newtonian approach to general relativity. A simple model is developed in
which the gravitomagnetic field of a localized mass-energy current varies
linearly with time. The implications of this temporal variation of the source
for the precession of test gyroscopes and the motion of null rays are briefly
discussed.Comment: 10 pages; v2: slightly expanded version accepted for publication in
Class. Quantum Gra
Oral Mucositis: An Update on Innate Immunity and New Interventional Targets
Oral mucositis (OM), a common debilitating toxicity associated with chemo- and radiation therapies, is a significant unmet clinical need for head and neck cancer patients. The biological complexities of chemoradiotherapy-induced OM involve interactions among disrupted tissue structures, inflammatory infiltrations, and oral microbiome, whereby several master inflammatory pathways constitute the complicated regulatory networks. Oral mucosal damages triggered by chemoradiotherapy-induced cell apoptosis were further exacerbated by the amplified inflammatory cascades dominantly governed by the innate immune responses. The coexistence of microbiome and innate immune components in oral mucosal barriers indicates that a signaling hub coordinates the interaction between environmental cues and host cells during tissue and immune homeostasis. Dysbiotic shifts in oral microbiota caused by cytotoxic cancer therapies may also contribute to the progression and severity of chemoradiotherapy-induced OM. In this review, we have updated the mechanisms involving innate immunity-governed inflammatory cascades in the pathobiology of chemoradiotherapy-induced OM and the development of new interventional targets for the management of this severe morbidity in head and neck cancer patients. © International & American Associations for Dental Research 2020
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