2,641 research outputs found
Conditions for Successful Extended Inflation
We investigate, in a model-independent way, the conditions required to obtain
a satisfactory model of extended inflation in which inflation is brought to an
end by a first-order phase transition. The constraints are that the correct
present strength of the gravitational coupling is obtained, that the present
theory of gravity is satisfactorily close to general relativity, that the
perturbation spectra from inflation are compatible with large scale structure
observations and that the bubble spectrum produced at the phase transition
doesn't conflict with the observed level of microwave background anisotropies.
We demonstrate that these constraints can be summarized in terms of the
behaviour in the conformally related Einstein frame, and can be compactly
illustrated graphically. We confirm the failure of existing models including
the original extended inflation model, and construct models, albeit rather
contrived ones, which satisfy all existing constraints.Comment: 8 pages RevTeX file with one figure incorporated (uses RevTeX and
epsf). Also available by e-mailing ARL, or by WWW at
http://star-www.maps.susx.ac.uk/papers/infcos_papers.html; Revised to include
extra references, results unchanged, to appear Phys Rev
The effect of two-temperature post-shock accretion flow on the linear polarization pulse in magnetic cataclysmic variables
The temperatures of electrons and ions in the post-shock accretion region of
a magnetic cataclysmic variable (mCV) will be equal at sufficiently high mass
flow rates or for sufficiently weak magnetic fields. At lower mass flow rates
or in stronger magnetic fields, efficient cyclotron cooling will cool the
electrons faster than the electrons can cool the ions and a two-temperature
flow will result. Here we investigate the differences in polarized radiation
expected from mCV post-shock accretion columns modeled with one- and
two-temperature hydrodynamics. In an mCV model with one accretion region, a
magnetic field >~30 MG and a specific mass flow rate of ~0.5 g/cm/cm/s, along
with a relatively generic geometric orientation of the system, we find that in
the ultraviolet either a single linear polarization pulse per binary orbit or
two pulses per binary orbit can be expected, depending on the accretion column
hydrodynamic structure (one- or two-temperature) modeled. Under conditions
where the physical flow is two-temperature, one pulse per orbit is predicted
from a single accretion region where a one-temperature model predicts two
pulses. The intensity light curves show similar pulse behavior but there is
very little difference between the circular polarization predictions of one-
and two-temperature models. Such discrepancies indicate that it is important to
model some aspect of two-temperature flow in indirect imaging procedures, like
Stokes imaging, especially at the edges of extended accretion regions, were the
specific mass flow is low, and especially for ultraviolet data.Comment: Accepted for publication in Astrophysics & Space Scienc
Dynamical study on polaron formation in a metal/polymer/metal structure
By considering a metal/polymer/metal structure within a tight-binding
one-dimensional model, we have investigated the polaron formation in the
presence of an electric field. When a sufficient voltage bias is applied to one
of the metal electrodes, an electron is injected into the polymer chain, then a
self-trapped polaron is formed at a few hundreds of femtoseconds while it moves
slowly under a weak electric field (not larger than V/cm).
At an electric field between V/cm and V/cm,
the polaron is still formed, since the injected electron is bounded between the
interface barriers for quite a long time. It is shown that the electric field
applied at the polymer chain reduces effectively the potential barrier in the
metal/polymer interface
Embedding Flipped SU(5) into SO(10)
We embed the flipped SU(5) models into the SO(10) models. After the SO(10)
gauge symmetry is broken down to the flipped SU(5) \times U(1)_X gauge
symmetry, we can split the five/one-plets and ten-plets in the spinor
\mathbf{16} and \mathbf{\bar{16}} Higgs fields via the stable sliding singlet
mechanism. As in the flipped SU(5) models, these ten-plet Higgs fields can
break the flipped SU(5) gauge symmetry down to the Standard Model gauge
symmetry. The doublet-triplet splitting problem can be solved naturally by the
missing partner mechanism, and the Higgsino-exchange mediated proton decay can
be suppressed elegantly. Moreover, we show that there exists one pair of the
light Higgs doublets for the electroweak gauge symmetry breaking. Because there
exist two pairs of additional vector-like particles with similar
intermediate-scale masses, the SU(5) and U(1)_X gauge couplings can be unified
at the GUT scale which is reasonably (about one or two orders) higher than the
SU(2)_L \times SU(3)_C unification scale. Furthermore, we briefly discuss the
simplest SO(10) model with flipped SU(5) embedding, and point out that it can
not work without fine-tuning.Comment: RevTex4, 28 pages, 3 figures, typos correcte
Simpler Is Better-Calibration of Pipe Roughness in Water Distribution Systems
Published: 17 October 2022Hydraulic models of water distribution systems (WDSs) need to be calibrated, so they can be used to help to make informed decisions. Usually, hydraulic model calibration follows an iterative process of comparing the simulation results from the model with field observations and making adjustments to model parameters to make sure an acceptable level of agreement between predicted and measured values (e.g., water pressure) has been achieved. However, the manual process can be time-consuming, and the termination criterion relies on the modeler’s judgment. Therefore, various optimization-based calibration methods have been developed. In this study, three different optimization methods, i.e., Sequential Least Squares Programming (SLSQP), a Genetic Algorithm (GA) and Differential Evolution (DE), are compared for calibrating the pipe roughness of WDS models. Their performance is investigated over four different decision variable set formulations with different levels of discretization of the search space. Results obtained from a real-world case study demonstrate that compared to traditional engineering practice, optimization is effective for hydraulic model calibration. However, a finer search space discretization does not necessarily guarantee better results; and when multiple methods lead to similar performance, a simpler method is better. This study provides guidance on method and formulation selection for calibrating WDS models.Qi Zhao, Wenyan Wu, Angus R. Simpson and Ailsa Willi
Valence band photoemission from the GaN(0001) surface
A detailed investigation by one-step photoemission calculations of the
GaN(0001)-(1x1) surface in comparison with recent experiments is presented in
order to clarify its structural properties and electronic structure. The
discussion of normal and off-normal spectra reveals through the identified
surface states clear fingerprints for the applicability of a surface model
proposed by Smith et al. Especially the predicted metallic bonds are confirmed.
In the context of direct transitions the calculated spectra allow to determine
the valence band width and to argue in favor of one of two theoretical bulk
band structures. Furthermore a commonly used experimental method to fix the
valence band maximum is critically tested.Comment: 8 pages, 11 eps files, submitted to PR
Water distribution system design integrating behind-the-meter solar under long-term uncertainty
Water distribution systems (WDSs) are important urban water infrastructure supporting a wide range of human activities. Due to the significant amount of energy consumed by the WDS throughout its lifespan, the operation of WDSs may have a significant impact on the environment, affecting the sustainable development of cities into the future. Behind-the-metre (BTM) solar photovoltaic (PV) system integration has been considered an effective way to reduce the impact of WDSs on the environment. However, solar PV technology is developing rapidly. Combined with long-term changes in water demand driven by population growth and urbanisation, the design of a WDS considering BTM solar has become a more challenging task. In this study, the co-design of WDS integrating BTM solar PV systems under changing future conditions in terms of water demand and solar PV technology development is investigated. It has been found that the BTM solar PV system and the potential development in solar PV technology effectively improve the robustness of WDS design under uncertain future water demand. The outcomes of this study can be extended to guide infrastructure design to provide sustainable infrastructure for future cities, and therefore cities can continue to support human activities in deeply uncertain future.Jiayu Yao, Wenyan Wu, Angus R. Simpson, Behzad Rismanch
New Results for the Correlation Functions of the Ising Model and the Transverse Ising Chain
In this paper we show how an infinite system of coupled Toda-type nonlinear
differential equations derived by one of us can be used efficiently to
calculate the time-dependent pair-correlations in the Ising chain in a
transverse field. The results are seen to match extremely well long large-time
asymptotic expansions newly derived here. For our initial conditions we use new
long asymptotic expansions for the equal-time pair correlation functions of the
transverse Ising chain, extending an old result of T.T. Wu for the 2d Ising
model. Using this one can also study the equal-time wavevector-dependent
correlation function of the quantum chain, a.k.a. the q-dependent diagonal
susceptibility in the 2d Ising model, in great detail with very little
computational effort.Comment: LaTeX 2e, 31 pages, 8 figures (16 eps files). vs2: Two references
added and minor changes of style. vs3: Corrections made and reference adde
Mir-223 regulates the number and function of myeloid-derived suppressor cells in multiple sclerosis and experimental autoimmune encephalomyelitis
Myeloid-derived cells play important modulatory and effector roles in multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE). Myeloid-derived suppressor cells (MDSCs) are immature myeloid cells, composed of monocytic (MO) and polymorphonuclear (PMN) fractions, which can suppress T cell activities in EAE. Their role in MS remains poorly characterized. We found decreased numbers of circulating MDSCs, driven by lower frequencies of the MO-MDSCs, and higher MDSC expression of microRNA miR-223 in MS versus healthy subjects. To gain mechanistic insights, we interrogated the EAE model. MiR-223 knock out (miR-223 12/ 12) mice developed less severe EAE with increased MDSC numbers in the spleen and spinal cord compared to littermate controls. MiR-223 12/ 12 MO-MDSCs suppressed T cell proliferation and cytokine production in vitro and EAE in vivo more than wild-type MO-MDSCs. They also displayed an increased expression of critical mediators of MDSC suppressive function, Arginase-1(Arg1), and the signal transducer and activator of transcription 3 (Stat3), which herein, we demonstrate being an miR-223 target gene. Consistently, MDSCs from MS patients displayed decreased STAT3 and ARG1 expression compared with healthy controls, suggesting that circulating MDSCs in MS are not only reduced in numbers but also less suppressive. These results support a critical role for miR-223 in modulating MDSC biology in EAE and in MS and suggest potential novel therapeutic applications
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