4,849 research outputs found
The Circumstellar Structure and Excitation Effects around the Massive Protostar Cepheus A HW 2
We report SMA 335 GHz continuum observations with angular resolution of
~0.''3, together with VLA ammonia observations with ~1'' resolution toward Cep
A HW 2. We find that the flattened disk structure of the dust emission observed
by Patel et al. is preserved at the 0.''3 scale, showing an elongated structure
of ~$0.''6 size (450 AU) peaking on HW 2. In addition, two ammonia cores are
observed, one associated with a hot-core previously reported, and an elongated
core with a double peak separated by ~1.''3 and with signs of heating at the
inner edges of the gas facing HW 2. The double-peaked ammonia structure, as
well as the double-peaked CH3CN structure reported previously (and proposed to
be two independent hot-cores), surround both the dust emission as well as the
double-peaked SO2 disk structure found by Jimenez-Serra et al. All these
results argue against the interpretation of the elongated dust-gas structure as
due to a chance-superposition of different cores; instead, they imply that it
is physically related to the central massive object within a disk-protostar-jet
system.Comment: 12 pages, 3 figures; accepted for publication in the Astrophysical
Journa
Deformed Density Matrix and Generalized Uncertainty Relation in Thermodynamics
A generalization of the thermodynamic uncertainty relations is proposed. It
is done by introducing of an additional term proportional to the interior
energy into the standard thermodynamic uncertainty relation that leads to
existence of the lower limit of inverse temperature. The authors are of the
opinion that the approach proposed may lead to proof of these relations. To
this end, the statistical mechanics deformation at Planck scale. The
statistical mechanics deformation is constructed by analogy to the earlier
quantum mechanical results. As previously, the primary object is a density
matrix, but now the statistical one. The obtained deformed object is referred
to as a statistical density pro-matrix. This object is explicitly described,
and it is demonstrated that there is a complete analogy in the construction and
properties of quantum mechanics and statistical density matrices at Plank scale
(i.e. density pro-matrices). It is shown that an ordinary statistical density
matrix occurs in the low-temperature limit at temperatures much lower than the
Plank's. The associated deformation of a canonical Gibbs distribution is given
explicitly.Comment: 15 pages,no figure
Hilbert space of wormholes
Wormhole boundary conditions for the Wheeler--DeWitt equation can be derived
from the path integral formulation. It is proposed that the wormhole wave
function must be square integrable in the maximal analytic extension of
minisuperspace. Quantum wormholes can be invested with a Hilbert space
structure, the inner product being naturally induced by the minisuperspace
metric, in which the Wheeler--DeWitt operator is essentially self--adjoint.
This provides us with a kind of probabilistic interpretation. In particular,
giant wormholes will give extremely small contributions to any wormhole state.
We also study the whole spectrum of the Wheeler--DeWitt operator and its role
in the calculation of Green's functions and effective low energy interactions.Comment: 23 pages, 2 figures available upon request, REVTE
Exact bounds for distributed graph colouring
We prove exact bounds on the time complexity of distributed graph colouring.
If we are given a directed path that is properly coloured with colours, by
prior work it is known that we can find a proper 3-colouring in communication rounds. We close the gap between upper and
lower bounds: we show that for infinitely many the time complexity is
precisely communication rounds.Comment: 16 pages, 3 figure
Is there a problem with quantum wormhole states in N=1 Supergravity?
The issue concerning the existence of wormhole states in locally
supersymmetric minisuperspace models with matter is addressed. Wormhole states
are apparently absent in models obtained from the more general theory of N=1
supergravity with supermatter. A Hartle-Hawking type solution can be found,
even though some terms (which are scalar field dependent) cannot be determined
in a satisfactory way. A possible cause is investigated here. As far as the
wormhole situation is concerned, we argue here that the type of Lagrange
multipliers and fermionic derivative ordering used can make a difference. A
proposal is made for supersymmetric quantum wormholes to also be invested with
a Hilbert space structure, associated with a maximal analytical extension of
the corresponding minisuperspace.is concerned, we argue here that the type of
Lagrange multipliers and fermionic derivative ordering used can make a
difference. A proposal is made for supersymmetric quantum wormholes to also be
invested with a Hilbert space structure, associated with a maximal analytical
extension of the corresponding minisuperspace.Comment: 22 pages, TeX (some font problems may occur, just press Return),
Based on a essay submitted to the 1995 ravity Research Foundation Awards,
accepted in G.R.
Ultra-broadband photon pair preparation by spontaneous four wave mixing in dispersion-engineered optical fiber
We present a study of the spectral properties of photon pairs generated
through the process of spontaneous four wave mixing (SFWM) in single mode
fiber. Our analysis assumes narrowband pumps, which are allowed to be
frequency-degenerate or non-degenerate. Based on this analysis, we derive
conditions on the pump frequencies and on the fiber dispersion parameters which
guarantee the generation of ultra-broadband photon pairs. Such photon pairs are
characterized by: i) a very large degree of entanglement, and ii) a very high
degree of temporal synchronization between the signal and idler photons.
Through a numerical exercise, we find that the use of photonic crystal fiber
(PCF) facilitates the fulfilment of the conditions for ultra-broadband photon
pair generation; in particular, the spectral region in which emission occurs
can be adjusted to particular needs through an appropriate choice of the PCF
parameters. In addition, we present a novel quantum interference effect,
resulting from indistinguishable pathways to the same outcome, which can occur
when pumping a SFWM source with multiple spectral lines.Comment: 15 pages, 10 figures. To be published in Phys. Rev.
Dominant negative phenotype of Bacillus thuringiensis Cry1Ab, Cry11Aa and Cry4Ba mutants suggest hetero-oligomer formation among different Cry toxins.
Background - Bacillus thuringiensis Cry toxins are used worldwide in the control of different insect pests important in agriculture or in human health. The Cry proteins are pore-forming toxins that affect the midgut cell of target insects. It was shown that non-toxic Cry1Ab helix a-4 mutants had a dominant negative (DN) phenotype inhibiting the toxicity of wildtype Cry1Ab when used in equimolar or sub-stoichiometric ratios (1:1, 0.5:1, mutant:wt) indicating that oligomer formation is a key step in toxicity of Cry toxins. Methodology/Principal Findings - The DN Cry1Ab-D136N/T143D mutant that is able to block toxicity of Cry1Ab toxin, was used to analyze its capacity to block the activity against Manduca sexta larvae of other Cry1 toxins, such as Cry1Aa, Cry1Ac, Cry1Ca, Cry1Da, Cry1Ea and Cry1Fa. Cry1Ab-DN mutant inhibited toxicity of Cry1Aa, Cry1Ac and Cry1Fa. In addition, we isolated mutants in helix a-4 of Cry4Ba and Cry11Aa, and demonstrate that Cry4Ba-E159K and Cry11Aa-V142D are inactive and completely block the toxicity against Aedes aegypti of both wildtype toxins, when used at sub-stoichiometric ratios, confirming a DN phenotype. As controls we analyzed Cry1Ab-R99A or Cry11Aa-E97A mutants that are located in helix a-3 and are affected in toxin oligomerization. These mutants do not show a DN phenotype but were able to block toxicity when used in 10:1 or 100:1 ratios (mutant:wt) probably by competition of binding with toxin receptors. Conclusions/Significance - We show that DN phenotype can be observed among different Cry toxins suggesting that may interact in vivo forming hetero-oligomers. The DN phenotype cannot be observed in mutants affected in oligomerization, suggesting that this step is important to inhibit toxicity of other toxin
CO and CH3OH observations of the BHR71 outflows with APEX
Context : Highly-collimated outflows are believed to be the earliest stage in
outflow evolution, so their study is essential for understanding the processes
driving outflows. The BHR71 Bok globule is known to harbour such a
highly-collimated outflow, which is powered by a protostar belonging to a
protobinary system. Aims : We aimed at investigating the interaction of
collimated outflows with the ambient molecular cloud by using molecular
tracers. Methods : We mapped the BHR71 highly-collimated outflow in CO(3-2)
with the APEX telescope, and observed several bright points of the outflow in
the molecular transitions CO(4-3), 13CO(3-2), C18O(3-2), and CH3OH(7-6). We use
an LVG code to characterise the temperature enhancements in these regions.
Results : In our CO(3-2) map, the second outflow driven by IRS2, which is the
second source of the binary system, is completely revealed and shown to be
bipolar. We also measure temperature enhancements in the lobes. The CO and
methanol LVG modelling points to temperatures between 30 and 50K in the IRS1
outflow, while the IRS2 outflow seems to be warmer (up to 300K).Comment: 4 pages, 5 Figures, accepted by A&A Letters, to appear in the APEX
First results special issu
Fair and optimistic quantum contract signing
We present a fair and optimistic quantum contract signing protocol between
two clients that requires no communication with the third trusted party during
the exchange phase. We discuss its fairness and show that it is possible to
design such a protocol for which the probability of a dishonest client to cheat
becomes negligible, and scales as N^{-1/2}, where N is the number of messages
exchanged between the clients. Our protocol is not based on the exchange of
signed messages: its fairness is based on the laws of quantum mechanics. Thus,
it is abuse-free, and the clients do not have to generate new keys for each
message during the Exchange phase. We discuss a real-life scenario when the
measurement errors and qubit state corruption due to noisy channels occur and
argue that for real, good enough measurement apparatus and transmission
channels, our protocol would still be fair. Our protocol could be implemented
by today's technology, as it requires in essence the same type of apparatus as
the one needed for BB84 cryptographic protocol. Finally, we briefly discuss two
alternative versions of the protocol, one that uses only two states (based on
B92 protocol) and the other that uses entangled pairs, and show that it is
possible to generalize our protocol to an arbitrary number of clients.Comment: 11 pages, 2 figure
Quantum Electromagnetic Wormholes and Geometrical Description of the Electric Charge
I present and discuss a class of solutions of the Wheeler-de Witt equation
describing wormholes generated by coupling of gravity to the electromagnetic
field for Kantowski-Sachs and Bianchi I spacetimes. Since the electric charge
can be viewed as electric lines of force trapped in a finite region of
spacetime, these solutions can be interpreted as the quantum corresponding of
the Ein\-stein\--Ro\-sen\--Mis\-ner\--Whee\-ler electromagnetic geon.Comment: 13 pages, PLAIN TEX, Report No: SISSA 92/94/A (to appear in Phys.
Rev. D15
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