4,403 research outputs found
Ground-state properties of two-dimensional dimerized Heisenberg models
The purpose of this paper is to investigate the ground-state properties of
two-dimensional Heisenberg models on a square lattice with a given
dimerization. Our aim is threefold: First, we want to investigate the
dimensional transition from two to one dimension for three models consisting of
weakly coupled chains for large dimerizations. Simple scaling arguments show
that the interchain coupling is always relevant. The ground states of two of
these models therefore have one-dimensional nature only at the decoupling
point. The third considered model is more complicated, because it contains
additional relevant intrachain couplings leading to a gap as shown by scaling
arguments and numerical investigations. Second, we investigate at which point
the dimerization destroys the N\'eel ordered ground state of the isotropic
model. Within a mapping to a nonlinear sigma-model and linear spinwave theory
(LSWT) we conclude that the stability of the N\'eel ordered state depends on
the microscopic details of the model. Third, the considered models also can be
regarded as effective models for a spin system with spin-phonon coupling. This
leads to the question if a spin-Peierls transition, i.e. a gain of total energy
due to lattice distortion, is possible. LSWT shows that such a transition is
possible under certain conditions leading to a coexistence of long-range order
and spin-Peierls dimerization. We also find that the gain of magnetic energy is
largest for a stair-like distortion of the lattice.Comment: 13 pages, 11 figures, revte
Observations of red-giant variable stars by Aboriginal Australians
Aboriginal Australians carefully observe the properties and positions of
stars, including both overt and subtle changes in their brightness, for
subsistence and social application. These observations are encoded in oral
tradition. I examine two Aboriginal oral traditions from South Australia that
describe the periodic changing brightness in three pulsating, red-giant
variable stars: Betelgeuse (Alpha Orionis), Aldebaran (Alpha Tauri), and
Antares (Alpha Scorpii). The Australian Aboriginal accounts stand as the only
known descriptions of pulsating variable stars in any Indigenous oral tradition
in the world. Researchers examining these oral traditions over the last
century, including anthropologists and astronomers, missed the description of
these stars as being variable in nature as the ethnographic record contained
several misidentifications of stars and celestial objects. Arguably,
ethnographers working on Indigenous Knowledge Systems should have academic
training in both the natural and social sciences.Comment: The Australian Journal of Anthropology (2018
Could the extensive use of rare elements in renewable energy technologies become a cause for concern?
The energy transformation process beginning to take place in many countries as a response to climate change will reduce substantially the consumption of fossil fuels, but at the same time cause a large increase in the demand for other raw materials. Whereas it is difficult to estimate the quantities of, for example, iron, copper and aluminium required, the situation is somewhat simpler for the rare elements that might be needed in a sustainable energy economy based largely on photovoltaic sources, wind and possibly nuclear fusion. We consider briefly each of these technologies and discuss the supply risks associated with the rare elements required, if they were to be used in the quantities that might be required for a global energy transformation process. In passing, we point out the need in resource studies to define the terms “rare”, “scarce” and “critical” and to use them in a consistent way
The first high-amplitude delta Scuti star in an eclipsing binary system
We report the discovery of the first high-amplitude delta Scuti star in an
eclipsing binary, which we have designated UNSW-V-500. The system is an
Algol-type semi-detached eclipsing binary of maximum brightness V = 12.52 mag.
A best-fitting solution to the binary light curve and two radial velocity
curves is derived using the Wilson-Devinney code. We identify a late A spectral
type primary component of mass 1.49+/-0.02 M_sun and a late K spectral type
secondary of mass 0.33+/-0.02 M_sun, with an inclination of 86.5+/-1.0 degrees,
and a period of 5.3504751+/-0.0000006 d. A Fourier analysis of the residuals
from this solution is performed using PERIOD04 to investigate the delta Scuti
pulsations. We detect a single pulsation frequency of f_1 = 13.621+/-0.015 c/d,
and it appears this is the first overtone radial mode frequency. This system
provides the first opportunity to measure the dynamical mass for a star of this
variable type; previously, masses have been derived from stellar evolution and
pulsation models.Comment: 7 pages, 6 figures, 2 tables, for submission to MNRAS, v2: paper size
change, small typographical changes to abstrac
Tectonics of a K+ channel: The importance of the N-terminus for channel gating
AbstractThe small K+ channel Kcv represents the pore module of complex potassium channels. It was found that its gating can be modified by sensor domains, which are N-terminally coupled to the pore. This implies that the short N-terminus of the channel can transmit conformational changes from upstream sensors to the channel gates. To understand the functional role of the N-terminus in the context of the entire channel protein, we apply combinatorial screening of the mechanical coupling and long-range interactions in the Kcv potassium channel by reduced molecular models. The dynamics and mechanical connections in the channel complex show that the N-terminus is indeed mechanically connected to the pore domain. This includes a long rang coupling to the pore and the inner and outer transmembrane domains. Since the latter domains host the two gates of the channel, the data support the hypothesis that mechanical perturbation of the N-terminus can be transmitted to the channel gates. This effect is solely determined by the topology of the channel; sequence details only have an implicit effect on the coarse-grained dynamics via the fold and not through biochemical details at a smaller scale. This observation has important implications for engineering of synthetic channels on the basis of a K+ channel pore
sCR1sLeX reduces lung allograft ischemia-reperfusion injury but does not ameliorate acute rejection
Background: Combined inhibition of complement and leukocyte adhesion by sCR1sLeX reduces lung allograft dysfunction up to 24 h. In the present study its effect on graft function and acute rejection was evaluated up to 5 days after experimental transplantation. Methods: Orthotopic single left lung transplantation was performed in 35 male rats (Brown Norway to Fischer 344) after a total ischemic time of 20 h. Two groups were assessed after 1, 3, and 5 days post-transplant, respectively (n=5 per group and time point): controls vs. recipients which received 10 mg/kg sCR1sLeX 15 min prior to reperfusion. In addition, five animals received 10 mg/kg per day sCR1sLeX for 5 days. For blood gas analysis of the graft, the contralateral lung was occluded for 5 min to assess graft function. Lung grafts were flushed, and histological grading was performed in blinded fashion according to the International Society for Heart and Lung Transplantation criteria. Results: Graft PaO2 in recipients treated with sCR1sLeX was superior on day 1 (383±118 vs. 56±15 mmHg; P≪0.0001) and day 3 (446±48 vs. 231±108 mmHg; P≪0.0001). Five days after transplantation, no difference in PaO2 was found (61±28 vs. 83±31 mmHg; P=0.59). Repeated treatment with sCR1sLeX for 5 days did not improve PaO2 (64±5 mmHg; P=0.65 vs. control; P=0.93 vs. sCR1sLeX). At any time point, there was no difference in the degree of rejection between groups. Conclusions: In this model sCR1sLeX provided marked improvement of graft function up to 3 days, but inhibition of both complement system and selectin dependent leukocyte adhesion failed to protect against acute rejectio
Modeling an ontology on accessible evacuation routes for emergencies
Providing alert communication in emergency situations is vital to reduce the number of victims. However, this is a challenging goal for researchers and professionals due to the diverse pool of prospective users, e.g. people with disabilities as well as other vulnerable groups. Moreover, in the event of an emergency situation, many people could become vulnerable because of exceptional circumstances such as stress, an unknown environment or even visual impairment (e.g. fire causing smoke). Within this scope, a crucial activity is to notify affected people about safe places and available evacuation routes. In order to address this need, we propose to extend an ontology, called SEMA4A (Simple EMergency Alert 4 [for] All), developed in a previous work for managing knowledge about accessibility guidelines, emergency situations and communication technologies. In this paper, we introduce a semi-automatic technique for knowledge acquisition and modeling on accessible evacuation routes. We introduce a use case to show applications of the ontology and conclude with an evaluation involving several experts in evacuation procedures. © 2014 Elsevier Ltd. All rights reserved
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