1,973 research outputs found
Study of a model for the folding of a small protein
We describe the results obtained from an improved model for protein folding.
We find that a good agreement with the native structure of a 46 residue long,
five-letter protein segment is obtained by carefully tuning the parameters of
the self-avoiding energy. In particular we find an improved free-energy
profile. We also compare the efficiency of the multidimensional replica
exchange method with the widely used parallel tempering.Comment: typos corrected, one figure adde
Upper limits of particle emission from high-energy collision and reaction near a maximally rotating Kerr black hole
The center-of-mass energy of two particles colliding near the horizon of a
maximally rotating black hole can be arbitrarily high if the angular momentum
of either of the incident particles is fine-tuned, which we call a critical
particle. We study particle emission from such high-energy collision and
reaction in the equatorial plane fully analytically. We show that the
unconditional upper limit of the energy of the emitted particle is given by
218.6% of that of the injected critical particle, irrespective of the details
of the reaction and this upper limit can be realized for massless particle
emission. The upper limit of the energy extraction efficiency for this emission
as a collisional Penrose process is given by 146.6%, which can be realized in
the collision of two massive particles with optimized mass ratio. Moreover, we
analyze perfectly elastic collision, Compton scattering, and pair annihilation
and show that net positive energy extraction is really possible for these three
reactions. The Compton scattering is most efficient among them and the
efficiency can reach 137.2%. On the other hand, our result is qualitatively
consistent with the earlier claim that the mass and energy of the emitted
particle are at most of order the total energy of the injected particles and
hence we can observe neither super-heavy nor super-energetic particles.Comment: 22 pages, 3 figures, typos corrected, reference updated, accepted for
publication in Physical Review D, typos correcte
Efficient optical quantum information processing
Quantum information offers the promise of being able to perform certain
communication and computation tasks that cannot be done with conventional
information technology (IT). Optical Quantum Information Processing (QIP) holds
particular appeal, since it offers the prospect of communicating and computing
with the same type of qubit. Linear optical techniques have been shown to be
scalable, but the corresponding quantum computing circuits need many auxiliary
resources. Here we present an alternative approach to optical QIP, based on the
use of weak cross-Kerr nonlinearities and homodyne measurements. We show how
this approach provides the fundamental building blocks for highly efficient
non-absorbing single photon number resolving detectors, two qubit parity
detectors, Bell state measurements and finally near deterministic control-not
(CNOT) gates. These are essential QIP devicesComment: Accepted to the Journal of optics B special issue on optical quantum
computation; References update
Quantum Dynamics of Three Coupled Atomic Bose-Einstein Condensates
The simplest model of three coupled Bose-Einstein Condensates (BEC) is
investigated using a group theoretical method. The stationary solutions are
determined using the SU(3) group under the mean field approximation. This
semiclassical analysis using the system symmetries shows a transition in the
dynamics of the system from self trapping to delocalization at a critical value
for the coupling between the condensates. The global dynamics are investigated
by examination of the stable points and our analysis shows the structure of the
stable points depends on the ratio of the condensate coupling to the
particle-particle interaction, undergoes bifurcations as this ratio is varied.
This semiclassical model is compared to a full quantum treatment, which also
displays the dynamical transition. The quantum case has collapse and revival
sequences superposed on the semiclassical dynamics reflecting the underlying
discreteness of the spectrum. Non-zero circular current states are also
demonstrated as one of the higher dimensional effects displayed in this system.Comment: Accepted to PR
Weak nonlinearities: A new route to optical quantum computation
Quantum information processing (QIP) offers the promise of being able to do
things that we cannot do with conventional technology. Here we present a new
route for distributed optical QIP, based on generalized quantum non-demolition
measurements, providing a unified approach for quantum communication and
computing. Interactions between photons are generated using weak
non-linearities and intense laser fields--the use of such fields provides for
robust distribution of quantum information. Our approach requires only a
practical set of resources, and it uses these very efficiently. Thus it
promises to be extremely useful for the first quantum technologies, based on
scarce resources. Furthermore, in the longer term this approach provides both
options and scalability for efficient many-qubit QIP.Comment: 7 Pages, 4 Figure
Quadrupolar effect and rattling motion in heavy fermion superconductor PrOs_4Sb_{12}
The elastic properties of a filled skutterudite PrOs_4Sb_{12} with a heavy
Fermion superconductivity at T_C=1.85 K have been investigated. The elastic
softening of (C_{11}-C_{12})/2 and C_{44} with lowering temperature down to T_C
indicates that the quadrupolar fluctuation due to the CEF state plays a role
for the Cooper paring in superconducting phase of PrOs_4Sb_{12}. A Debye-type
dispersion in the elastic constants around 30 K revealed a thermally activated
Gamma_{23} rattling due to the off-center Pr-atom motion obeying
tau=tau_{0}exp(E/k_{B}T) with an attempt time tau_0=8.8*10^{-11} sec and an
activation energy E=168 K. It is remarkable that the charge fluctuation of the
off-center motion with Gamma_{23} symmetry may mix with the quadrupolar
fluctuation and enhance the elastic softening of (C_{11}-C_{12})/2 just above
T_C.Comment: 5 pages, 4 figures, to be published to Phys. Rev.
Monitoring of emerging micropollutants in hydric media in Bragança district
Emerging Micropollutants are a subclass of Pollutants and they can be
classified as Persistent Organic Pollutants, Endocrine Disrupting Compounds and Pharmaceuticals and Personal Care Products (PPCP´s). These compounds may cause undesired effects to health or to the environment when used in high quantities or wrong ways. Generally, a pharmaceutical drug is prescribed to cause the desired therapeutic effect. However after their use, even at low concentrations they can retain their physicochemical properties [1].
Because of these effects, among others, PPCP’s are substances excreted in
relevant quantities by the human body and are not effectively removed from water in sewage treatment plants [2].info:eu-repo/semantics/publishedVersio
Extraction and quantification of pharmaceutical drugs in aqueous matrices
The increasing production and use of chemical compounds, coupled with inefficient sewage treatment systems, results in an inadequate release of all types of pollutants into
the environment.
Emerging pollutants are potentially toxic substances normally found in very small concentrations but that can produce harmful effects on the environment. These
compounds are not yet included in water quality monitoring programs nor in environmental control legislation standards.
Pharmaceutical and Personal Care Products (PPCPs) are an important group of emerging pollutants due to their continuing increase in world consumption and their
inherent capacity to induce physiological effects at very low doses, raising concerns about potential adverse effects in humans, animals and environmental systems.info:eu-repo/semantics/publishedVersio
Magnetic-Field-Independent Ultrasonic Dispersions in the Magnetically Robust Heavy Fermion System SmOs4Sb12
Elastic properties of the filled skutterudite compound SmOsSb have
been investigated by ultrasonic measurements. The elastic constant
shows two ultrasonic dispersions at 15 K and 53 K
for frequencies between 33 and 316 MHz, which follow a Debye-type
formula with Arrhenius-type temperature-dependent relaxation times, and remain
unchanged even with applied magnetic fields up to 10 T. The corresponding
activation energies were estimated to be = 105 K and = 409 K,
respectively. The latter, , is the highest value reported so far in the
Sb-based filled skutterudites. The presence of magnetically robust ultrasonic
dispersions in SmOsSb implies a possibility that an emergence of a
magnetically insensitive heavy fermion state in this system is associated with
a novel local charge degree of freedom which causes the ultrasonic dispersion.Comment: 5 pages, 4 figure
A Stable Routing Protocol to Support ITS Services in VANET Networks
科研費報告書収録論文(課題番号:17500030/研究代表者:加藤寧/インターネットと高親和性を有する次世代低軌道衛星ネットワークに関する基盤研究
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