2,126 research outputs found
Estimating the mass of the debris disc in HD 69830
We present a method to estimate the mass of the debris disc in the HD 69830
system, which also hosts three exoplanets with Neptune-like minimum masses. By
considering the range of published stellar ages, we interpret the infrared
emission from the debris disc as originating from a steady state, collisional
cascade of dust grains. Using dynamical survival models subjected to
observational constraints, we estimate the allowed range of disc masses. If the
disc has an age of about 1 Gyr, then its mass is several times that of our
asteroid belt. The maximum allowed age for the disc and the number of
planetesimals it contains are determined by the assumed value for the binding
energy of the planetesimals. If one insists on interpreting the disc as being
transient, then this mass estimate becomes an upper limit.Comment: Accepted by MNRAS. 4 pages, 2 figures. No changes from previous
version, except for corrections of typographical errors and to British
English (e.g., "disc"
Dispersion of Ripplons in Superfluid 4he
A detailed study of the dispersion law of surface excitations in liquid \hef
at zero temperature is presented, with special emphasis to the short wave
length region. The hybridization mechanism between surface and bulk modes is
discussed on a general basis, investigating the scattering of slow rotons from
the surface. An accurate density functional, accounting for backflow effects,
is then used to determine the dispersion of both bulk and surface excitations.
The numerical results are close to the experimental data obtained on thick
films and explicitly reveal the occurrence of important hybridization effects
between ripplons and rotons.Comment: 23 pages, REVTEX 3.0, 11 figures upon request, UTF-326/9
In vitro culturing of porcine tracheal mucosa as an ideal model for investigating the influence of drugs on human respiratory mucosa
It has been previously shown that fresh mucosa from different mammals could serve as raw material for in vitro culturing with the differentiation of cilia, which are the most important morphological structures for the function of the mucociliary system. Increasing legal restrictions on the removal of human tissue and changing surgical techniques have led to a lack of fresh human mucosa for culturing. Most of the animals that have been used as donors up to now are genetically not very close to human beings and must all be sacrificed for such studies. We, therefore, established a modified system of culturing mucosa cells from the trachea of pigs, which is available as a regular by-product after slaughtering. With respect to the possibility of developing “beating” cilia, it could be shown that the speed of cell proliferation until adhesion to the coated culture dishes, the formation of conjunctions of cell clusters and the proliferation of cilia were comparable for porcine and human mucosa. Moreover, it could be demonstrated that the porcine cilia beat frequency of 7.57 ± 1.39 Hz was comparable to the human mucosa cells beat frequency of 7.3 ± 1.4 Hz and that this beat frequency was absolutely constant over the investigation time of 360 min. In order to prove whether the reaction to different drugs is comparable between the porcine and human cilia, we initially tested benzalkonium chloride, which is known to be toxic for human cells, followed by naphazoline, which we found in previous studies on human mucosa to be non-toxic. The results clearly showed that the functional and morphological reactions of the porcine ciliated cells to these substances were similar to the reaction we found in the in vitro cultured human mucosa
Terrestrial Planet Formation in the Inclined Systems: Application to OGLE-2006-BLG-109L System
In this work, we extensively investigate the terrestrial planetary formation
for the inclined planetary systems (considering the OGLE-2006-BLG-109L system
as prototype) in the late stage. In the simulations, we show that the
occurrence of terrestrial planets is quite common, in the final assembly stage.
Moreover, we find that 40% of the runs finally occupy one planet in the
habitable zone (HZ). On the other hand, the numerical results also indicate
that the inner region of the planetesimal disk, ranging from to 0.3
AU, plays an important role in building up terrestrial planets. By examining
all simulations, we note that the survivals are located either between
0.11.0 AU or beyond 7 AU, or at the 1:1 mean motion resonance of
OGLE-2006-BLG-109Lb at 2.20 AU. The outcomes suggest that it may exist
moderate possibility for the inclined systems to harbor terrestrial planets,
even planets in the HZs.Comment: 13 pages, 9 figures, accepted for publication in MNRA
Kondo effect in nanostructures
Kondo effect arises whenever a coupling to the Fermi gas induces transitions
within the otherwise degenerate ground state multiplet of an interacting
system. Both coupling to the Fermi gas and interactions are naturally present
in any nanoscale transport experiment. At the same time, many nanostructures
can easily be tuned to the vicinity of a degeneracy point. This is why the
Kondo effect in its various forms often influences the low temperature
transport in meso- and nanoscale systems.
In this short review we discuss the basic physics of the Kondo effect and its
manifestations in the low-temperature electronic transport through a single
electron transistor
Toward Improved Environmental Stability of Polymer:Fullerene and Polymer:Nonfullerene Organic Solar Cells: A Common Energetic Origin of Light- and Oxygen-Induced Degradation
With the emergence of nonfullerene electron acceptors resulting in further breakthroughs in the performance of organic solar cells, there is now an urgent need to understand their degradation mechanisms in order to improve their intrinsic stability through better material design. In this study, we present quantitative evidence for a common root cause of light-induced degradation of polymer:nonfullerene and polymer:fullerene organic solar cells in air, namely, a fast photo-oxidation process of the photoactive materials mediated by the formation of superoxide radical ions, whose yield is found to be strongly controlled by the lowest unoccupied molecular orbital (LUMO) levels of the electron acceptors used. Our results elucidate the general relevance of this degradation mechanism to both polymer:fullerene and polymer:nonfullerene blends and highlight the necessity of designing electron acceptor materials with sufficient electron affinities to overcome this challenge, thereby paving the way toward achieving long-term solar cell stability with minimal device encapsulation
Kondo effect in coupled quantum dots: a Non-crossing approximation study
The out-of-equilibrium transport properties of a double quantum dot system in
the Kondo regime are studied theoretically by means of a two-impurity Anderson
Hamiltonian with inter-impurity hopping. The Hamiltonian, formulated in
slave-boson language, is solved by means of a generalization of the
non-crossing approximation (NCA) to the present problem. We provide benchmark
calculations of the predictions of the NCA for the linear and nonlinear
transport properties of coupled quantum dots in the Kondo regime. We give a
series of predictions that can be observed experimentally in linear and
nonlinear transport measurements through coupled quantum dots. Importantly, it
is demonstrated that measurements of the differential conductance , for the appropriate values of voltages and inter-dot tunneling
couplings, can give a direct observation of the coherent superposition between
the many-body Kondo states of each dot. This coherence can be also detected in
the linear transport through the system: the curve linear conductance vs
temperature is non-monotonic, with a maximum at a temperature
characterizing quantum coherence between both Kondo states.Comment: 20 pages, 17 figure
Duodenal gastric metaplasia and Helicobacter pylori infection in patients with diffuse nodular duodenitis
Macaque models of human infectious disease.
Macaques have served as models for more than 70 human infectious diseases of diverse etiologies, including a multitude of agents-bacteria, viruses, fungi, parasites, prions. The remarkable diversity of human infectious diseases that have been modeled in the macaque includes global, childhood, and tropical diseases as well as newly emergent, sexually transmitted, oncogenic, degenerative neurologic, potential bioterrorism, and miscellaneous other diseases. Historically, macaques played a major role in establishing the etiology of yellow fever, polio, and prion diseases. With rare exceptions (Chagas disease, bartonellosis), all of the infectious diseases in this review are of Old World origin. Perhaps most surprising is the large number of tropical (16), newly emergent (7), and bioterrorism diseases (9) that have been modeled in macaques. Many of these human diseases (e.g., AIDS, hepatitis E, bartonellosis) are a consequence of zoonotic infection. However, infectious agents of certain diseases, including measles and tuberculosis, can sometimes go both ways, and thus several human pathogens are threats to nonhuman primates including macaques. Through experimental studies in macaques, researchers have gained insight into pathogenic mechanisms and novel treatment and vaccine approaches for many human infectious diseases, most notably acquired immunodeficiency syndrome (AIDS), which is caused by infection with human immunodeficiency virus (HIV). Other infectious agents for which macaques have been a uniquely valuable resource for biomedical research, and particularly vaccinology, include influenza virus, paramyxoviruses, flaviviruses, arenaviruses, hepatitis E virus, papillomavirus, smallpox virus, Mycobacteria, Bacillus anthracis, Helicobacter pylori, Yersinia pestis, and Plasmodium species. This review summarizes the extensive past and present research on macaque models of human infectious disease
Search for Kaluza-Klein Graviton Emission in Collisions at TeV using the Missing Energy Signature
We report on a search for direct Kaluza-Klein graviton production in a data
sample of 84 of \ppb collisions at = 1.8 TeV, recorded
by the Collider Detector at Fermilab. We investigate the final state of large
missing transverse energy and one or two high energy jets. We compare the data
with the predictions from a -dimensional Kaluza-Klein scenario in which
gravity becomes strong at the TeV scale. At 95% confidence level (C.L.) for
=2, 4, and 6 we exclude an effective Planck scale below 1.0, 0.77, and 0.71
TeV, respectively.Comment: Submitted to PRL, 7 pages 4 figures/Revision includes 5 figure
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