5,085 research outputs found
Source amplitudes for active exterior cloaking
The active cloak comprises a discrete set of multipole sources that
destructively interfere with an incident time harmonic scalar wave to produce
zero total field over a finite spatial region. For a given number of sources
and their positions in two dimensions it is shown that the multipole amplitudes
can be expressed as infinite sums of the coefficients of the incident wave
decomposed into regular Bessel functions. The field generated by the active
sources vanishes in the infinite region exterior to a set of circles defined by
the relative positions of the sources. The results provide a direct solution to
the inverse problem of determining the source amplitudes. They also define a
broad class of non-radiating discrete sources.Comment: 21 pages, 17 figure
Effects of lattice distortion and Jahn–Teller coupling on the magnetoresistance of La0.7Ca0.3MnO3 and La0.5Ca0.5CoO3 epitaxial films
Studies of La0.7Ca0.3MnO3 epitaxial films on substrates with a range of lattice constants reveal two dominant contributions to the occurrence of colossal negative magnetoresistance (CMR) in these manganites: at high temperatures (T → TC, TC being the Curie temperature), the magnetotransport properties are predominantly determined by the conduction of lattice polarons, while at low temperatures (T ≪ TC/, the residual negative magnetoresistance is correlated with the substrate-induced lattice distortion which incurs excess magnetic domain wall scattering. The importance of lattice polaron conduction associated with the presence of Jahn–Teller coupling in the manganites is further verified by comparing the manganites with epitaxial films of another ferromagnetic perovskite, La0.5Ca0.5CoO3. Regardless of the differences in the substrate-induced lattice distortion, the cobaltite films exhibit much smaller negative magnetoresistance, which may be attributed to the absence of Jahn–Teller coupling and the high electron mobility that prevents the formation of lattice polarons. We therefore suggest that lattice polaron conduction associated with the Jahn–Teller coupling is essential for the occurrence of CMR, and that lattice distortion further enhances the CMR effects in the manganites
Loop-induced photon spectral lines from neutralino annihilation in the NMSSM
We have computed the loop-induced processes of neutralino annihilation into
two photons and, for the first time, into a photon and a Z boson in the
framework of the NMSSM. The photons produced from these radiative modes are
monochromatic and possess a clear "smoking gun" experimental signature. This
numerical analysis has been done with the help of the SloopS code, initially
developed for automatic one-loop calculation in the MSSM. We have computed the
rates for different benchmark points coming from SUGRA and GMSB soft SUSY
breaking scenarios and compared them with the MSSM. We comment on how this
signal can be enhanced, with respect to the MSSM, especially in the low mass
region of the neutralino. We also discuss the possibility of this observable to
constrain the NMSSM parameter space, taking into account the latest limits from
the FERMI collaboration on these two modes.Comment: 18 pages, 3 figures. Minor clarifications added in the text. Typing
mistakes and references corrected. Matches published versio
Spectroscopic Evidence for Anisotropic S-Wave Pairing Symmetry in MgB2
Scanning tunneling spectroscopy of superconducting MgB ( K)
were studied on high-density pellets and c-axis oriented films. The sample
surfaces were chemically etched to remove surface carbonates and hydroxides,
and the data were compared with calculated spectra for all symmetry-allowed
pairing channels. The pairing potential () is best described by an
anisotropic s-wave pairing model, with , where is the angle relative to the
crystalline c-axis, meV, and meV.Comment: 4 pages and 3 figures. Submitted to Physical Review Letters.
Corresponding author: Nai-Chang Yeh (e-mail: [email protected]
Millikelvin magnetic relaxation measurements of alpha-Fe2O3 antiferromagnetic particles
In this paper we report magnetic relaxation data for antiferromagnetic
alpha-Fe2O3 particles of 5 nm mean diameter in the temperature range 0.1 K to
25 K. The average spin value of these particles S=124 and the uniaxial
anisotropy constant D=1.6x10^-2 K have been estimated from the experimental
values of the blocking temperature and anisotropy field. The observed plateau
in the magnetic viscosity from 3 K down to 100 mK agrees with the occurrence of
spin tunneling from the ground state Sz = S. However, the scaling M vs Tln(nu
t) is broken below 5 K, suggesting the occurrence of tunneling from excited
states below this temperature.Comment: 4 pages (two columns), 4 figure
Biological activities of 13, 28-epoxyoleanane triterpene saponins from two peruvian Myrsinaceae
Two known 13,28-epoxy-oleanane triterpene saponins (1) and (2), were isolated from the 95% ethanolic extract of the roots of Myrsine coriaceae and Myrsine andina. Their structures were deduced by combined spectral analysis and chemical evidences based on data reported in the literature. Compounds 1 and 2 were evaluated in vitro against different cellular models such as Mycobacterium tuberculosis, Leishmania amazonensis axenic amastigotes, six human cancer cell lines (Hs683, T98G, U251, HT29, MCF7, SKMEL28) and two murine cell lines (CT26 and B16F10). Compound 1 was found to exhibit antileishmanial activity (IC50 = 16 µg/mL) whereas compound 2 was inactive (IC50 > 50 µg/mL). Furthermore, compound 1 exhibited stronger inhibition activity on human cancer cells (IC50 = 15 µg/mL) and on murine cell lines (IC50 = 10 µg/mL) than compound 2 (IC50 > 82 and 42 µg/mL, respectively). As the only difference between 1 and 2 is due to a substitution of an aldehyde group by a hydroxymethyl moiety, these results showed the crucial role of the aldehyde function at C-30 for the cytotoxicity. In contrast, none of the tested compounds revealed activity against M. tuberculosis
Lighting conditions in home office and occupant's perception: Exploring drivers of satisfaction
This paper depicts lighting home office conditions within different countries and continents, emphasizing the user's satisfaction with the visual environment. The scope of this article is to investigate the drivers of participants' satisfaction with the lighting conditions at the home office. The study was developed by a team of international experts working together on Subtask A: User perspective and requirements, Task 61 IEA (International Energy Agency): Solutions for daylighting and electric lighting. An online survey was launched in December 2020 and closed on March 2021. The survey was implemented in the native languages of six participant countries (Brazil, Colombia, Denmark, Italy, Poland, and Japan) using Google Forms, and its dissemination was via various social media platforms. Measures of association between variables and predictive tests were run to explore which investigated aspects drove participants' satisfaction with the lighting conditions at the home office. We found some differences in satisfaction due to participants' sex, occupation, and participants' continent of residence. Females were more satisfied with daylight than males. Associations between the perception of seven light descriptors and satisfaction showed differences between East Asians and the rest of the participants, which might be related to the high dependence of the formers on electric lighting even when daylight is available. Design features as southern facades, the distance from the working area to the window, type of internal sun shading were related to daylighting satisfaction. Moreover, satisfaction with the general light level and the electric light was higher for those participants who did not need to switch on the ceiling, floor, or desk lamp when daylight was available. We found that an external view composed of 3 layers and the sky's visibility afforded a higher satisfaction with the window view. Having an independent room for the home office appeared to be related to a higher willingness to continue in the home office. Likewise, higher satisfaction with the overall visual environment and window view appeared to increase the willingness to continue working from home. Bridging the gap amid cultural differences and daylighting and lighting satisfaction is needed, particularly, relational studies between design features –as a response of cultural, climatic, and local practices- and occupants' preferences and acceptability. Thus, our understanding of occupants' responses will be more comprehensive. Engaging further research and measures to improve the visual environment and overall indoor environmental quality in dwellings is now a necessary step
Light neutralino dark matter in the MSSM and its implication for LHC searches for staus
It was shown in a previous study that a lightest neutralino with mass below
30 GeV was severely constrained in the minimal supersymmetric standard model
(MSSM), unless it annihilates via a light stau and thus yields the observed
dark matter abundance. In such a scenario, while the stau is the
next-to-lightest supersymmetric particle (NLSP), the charginos and the other
neutralinos as well as sleptons of the first two families are also likely to be
not too far above the mass bounds laid down by the Large Electron Positron
(LEP) collider. As the branching ratios of decays of the charginos and the
next-to-lightest neutralino into staus are rather large, one expects
significant rates of tau-rich final states in such a case. With this in view,
we investigate the same-sign ditau and tri-tau signals of this scenario at the
Large Hadron Collider (LHC) for two MSSM benchmark points corresponding to
light neutralino dark matter. The associated signal rates for these channels
are computed, for the centre-of-mass energy of 14 TeV. We find that both
channels lead to appreciable rates if the squarks and the gluino are not too
far above a TeV, thus allowing to probe scenarios with light neutralinos in the
14 TeV LHC run with 10-100 fb^{-1}.Comment: 19p, 4 Fig
A conical deficit in the AdS4/CFT3 correspondence
Inspired by the AdS/CFT correspondence we propose a new duality that allow
the study of strongly coupled field theories living in a 2+1 conical
space-time. Solving the 4-d Einstein equations in the presence of an infinite
static string and negative cosmological constant we obtain a conical AdS4
space-time whose boundary is identified with the 2+1 cone found by Deser,
Jackiw and 't Hooft. Using the AdS4/CFT3 correspondence we calculate retarded
Green's functions of scalar operators living in the cone.Comment: v3, 14 pages. We reinterpret our results for the Green's functions in
the con
An international network to monitor the structure, composition and dynamics of Amazonian forests (RAINFOR)
The Amazon basin is likely to be increasingly affected by environmental changes: higher temperatures, changes in precipitation, CO2 fertilization and habitat fragmentation. To examine the important ecological and biogeochemical consequences of these changes, we are developing an international network, RAINFOR, which aims to monitor forest biomass and dynamics across Amazonia in a co-ordinated fashion in order to understand their relationship to soil and climate. The network will focus on sample plots established by independent researchers, some providing data extending back several decades. We will also conduct rapid transect studies of poorly monitored regions. Field expeditions analysed local soil and plant properties in the first phase (2001–2002). Initial results suggest that the network has the potential to reveal much information on the continental-scale relations between forest and environment. The network will also serve as a forum for discussion between researchers, with the aim of standardising sampling techniques and methodologies that will enable Amazonian forests to be monitored in a coherent manner in the coming decades
- …