179 research outputs found
A geometric interpretation of the spectral parameter for surfaces of constant mean curvature
Considering the kinematics of the moving frame associated with a constant
mean curvature surface immersed in S^3 we derive a linear problem with the
spectral parameter corresponding to elliptic sinh-Gordon equation. The spectral
parameter is related to the radius R of the sphere S^3. The application of the
Sym formula to this linear problem yields constant mean curvature surfaces in
E^3. Independently, we show that the Sym formula itself can be derived by an
appropriate limiting process R -> infinity.Comment: 12 page
Classical and quantum dynamics of confined test particles in brane gravity
A model is constructed for the confinement of test particles moving on a
brane. Within the classical framework of this theory, confining a test particle
to the brane eliminates the effects of extra dimensions, rendering them
undetectable. However, in the quantized version of the theory, the effects of
the gauge fields and extrinsic curvature are pronounced and this might provide
a hint for detecting them. As a consequence of confinement the mass of the test
particle is shown to be quantized. The condition of stability against small
perturbations along extra dimensions is also studied and its relation to dark
matter is discussed.Comment: 15 pages, no figures, extended, references adde
Stabilization of test particles in Induced Matter Kaluza-Klein theory
The stability conditions for the motion of classical test particles in an -dimensional Induced Matter Kaluza-Klein theory is studied. We show that
stabilization requires a variance of the strong energy condition for the
induced matter to hold and that it is related to the hierarchy problem.
Stabilization of test particles in a FRW universe is also discussed.Comment: 15 pages, 1 figure, to appear in Class. Quantum Gra
Proximity Effect and Multiple Andreev Reflections in Chaotic Josephson junctions
We study the dc-current transport in a voltage biased superconductor-chaotic
dot-superconductor junction with an induced proximity effect(PE) in the dot. It
is found that for a Thouless energy of the dot smaller than the
superconducting energy gap , the PE is manifested as peaks in the
differential conductance at voltages of order away from the even
subharmonic gap structures . These peaks are
insensitive to temperatures but are suppressed by a weak
magnetic field. The current for suppressed PE is independent of and
magnetic field and is shown to be given by the Octavio-Tinkham-Blonder-Klapwijk
theory.Comment: 4 pages, 3 figure
Observation of Multi-Gap Superconductivity in GdO(F)FeAs by Andreev Spectroscopy
We have studied current-voltage characteristics of Andreev contacts in
polycrystalline GdOFFeAs samples with bulk critical
temperature = (52.5 \pm 1)K using break-junction technique. The data
obtained cannot be described within the single-gap approach and suggests the
existence of a multi-gap superconductivity in this compound. The large and
small superconducting gap values estimated at T = 4.2K are {\Delta}L = 10.5 \pm
2 meV and {\Delta}S = 2.3 \pm 0.4 meV, respectively.Comment: 5 pages, 4 figures, submitted to JETP Letter
Investigation of LiFeAs by means of "Break-junction" Technique
In our tunneling investigation using Andreev superconductor - normal metal -
superconductor contacts on LiFeAs single crystals we observed two reproducible
independent subharmonic gap structures at dynamic conductance characteristics.
From these results, we can derive the energy of the large superconducting gap
meV and the small gap meV at
K for the K (the contact area
critical temperature which deviation causes the variation of ). The
BCS-ratio is found to be , whereas
results from induced superconductivity in the bands
with the small gap.Comment: 7 pages, 5 figures. Published in Pis'ma v ZhETF 95, 604-610 (2012
Synthesis of γ-, Ύ-, and Δ-Lactams by Asymmetric Transfer Hydrogenation of N-(tert-Butylsulfinyl)iminoesters
Highly enantiomerically enriched Îł- and ÎŽ-lactams have been prepared by a simple and very efficient procedure that involves the asymmetric transfer hydrogenation of N-(tert-butylsulfinyl)iminoesters followed by desulfinylation of the nitrogen atom and spontaneous cyclization to the desired lactams during the basic workup procedure. Five- and six-membered ring lactams bearing aromatic, heteroaromatic, and aliphatic substituents have been obtained in very high yields and eeâs up to >99%. A slight modification of the procedure also allowed the preparation of Δ-lactams in good yields and very high enantioselectivities. Both enantiomers of the final lactams could be prepared with equal efficiency by changing the absolute configuration of the sulfinyl chiral auxiliary
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Establishment of Normal Gut Microbiota Is Compromised under Excessive Hygiene Conditions
Background: Early gut colonization events are purported to have a major impact on the incidence of infectious,
inflammatory and autoimmune diseases in later life. Hence, factors which influence this process may have important
implications for both human and animal health. Previously, we demonstrated strong influences of early-life environment on
gut microbiota composition in adult pigs. Here, we sought to further investigate the impact of limiting microbial exposure
during early life on the development of the pig gut microbiota.
Methodology/Principal Findings: Outdoor- and indoor-reared animals, exposed to the microbiota in their natural rearing
environment for the first two days of life, were transferred to an isolator facility and adult gut microbial diversity was
analyzed by 16S rRNA gene sequencing. From a total of 2,196 high-quality 16S rRNA gene sequences, 440 phylotypes were
identified in the outdoor group and 431 phylotypes in the indoor group. The majority of clones were assigned to the four
phyla Firmicutes (67.5% of all sequences), Proteobacteria (17.7%), Bacteroidetes (13.5%) and to a lesser extent,
Actinobacteria (0.1%). Although the initial maternal and environmental microbial inoculum of isolator-reared animals was
identical to that of their naturally-reared littermates, the microbial succession and stabilization events reported previously in
naturally-reared outdoor animals did not occur. In contrast, the gut microbiota of isolator-reared animals remained highly
diverse containing a large number of distinct phylotypes.
Conclusions/Significance: The results documented here indicate that establishment and development of the normal gut
microbiota requires continuous microbial exposure during the early stages of life and this process is compromised under
conditions of excessive hygiene
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