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971.
In this paper, we try to answer the following question: given a modular tensor category ? with an action of a compact group
G, is it possible to describe in a suitable sense the “quotient” category ?/G? We give a full answer in the case when ?=?ℯ? is the category of vector spaces; in this case, ?ℯ?/G turns out to be the category of representation of Drinfeld's double D(G). This should be considered as the category theory analog of the topological identity {pt}/G=BG.
This implies a conjecture of Dijkgraaf, Vafa, E. Verlinde and H. Verlinde regarding so-called orbifold conformal field theories:
if ? is a vertex operator algebra which has a unique irreducible module, ? itself, and G is a compact group of automorphisms of ?, and some not too restrictive technical conditions are satisfied, then G is finite, and the category of representations of the algebra of invariants, ?
G
, is equivalent as a tensor category to the category of representations of Drinfeld's double D(G). We also get some partial results in the non-holomorphic case, i.e. when ? has more than one simple module.
Received: 27 August 2001 / Accepted: 1 March 2002 相似文献
972.
We discuss the notion of spin squeezing considering two mutually exclusive classes of spin-s states, namely, oriented and non-oriented states. Our analysis shows that the oriented states are not squeezed while non-oriented
states exhibit squeezing. We also present a new scheme for construction of spin-s states using 2s spinors oriented along different axes. Taking the case of s=1, we show that the ‘non-oriented’ nature and hence squeezing arise from the intrinsic quantum correlations that exist among
the spinors in the coupled state. 相似文献
973.
Yasuyuki Kawahigashi 《Communications in Mathematical Physics》2002,226(2):269-287
We study the recent construction of subfactors by Rehren which generalizes the Longo–Rehren subfactors. We prove that if
we apply this construction to a non-degenerately braided subfactor N⊂M and α±-induction, then the resulting subfactor is dual to the Longo–Rehren subfactor M⊗M
opp⊂R arising from the entire system of irreducible endomorphisms of M resulting from αplusmn;-induction. As a corollary, we solve a problem on existence of braiding raised by Rehren negatively. Furthermore, we generalize
our previous study with Longo and Müger on multi-interval subfactors arising from a completely rational conformal net of factors
on S
1 to a net of subfactors and show that the (generalized) Longo–Rehren subfactors and α-induction naturally appear in this context.
Received: 11 September 2001 / Accepted: 7 October 2001 相似文献
974.
In this paper we report some of the important results of experimental investigations of the flicker noise near the metal-insulator
(MI) transition in doped silicon single crystals. This is the first comprehensive work to study low-frequency noise in heavily
doped Si over an extensive temperature range (2 K<T<500 K). The measurements of conductance fluctuations (flicker noise) were carried out in the frequency range 10−2<f<4 × 101 Hz in single crystalline Si across the MI transition by doping with phosphorous and boron. The magnitude of noise in heavily
doped Si is much larger than that seen in lightly doped Si over the whole temperature range. The extensive temperature range
covered allowed us to detect two distinct noise mechanisms. At low temperatures (T<100 K) universal conductance fluctuations (UCF) dominate and the spectral dependence of the noise is determined by dephasing
the electron from defects with two-levels (TLS). At higher temperatures (T>200 K) the noise arises from activated defect dynamics. As the MI transition is approached, the 1/f spectral power, typical of the metallic regime, gets modified by the presence of discrete Lorentzians which arise from generation-recombination
process which is the characteristic of a semiconductor. 相似文献
975.
Ben-Yuan Gu Yao Lu Tzong-Jer Yang 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):493-502
We present numerical investigations of the transmission properties of electrons in a normal quantum wire tangentially attached
to a superconductor ring threaded by magnetic flux. A point scatterer with a δ -function potential is placed at node to model
scattering effect. We find that the transmission characteristics of electrons in this structure strongly depend on the normal
or superconducting state of the ring. The transmission probability as a function of the energy of incident electrons, in the
case of a superconductor ring threaded by one quantum magnetic flux, emerges one deep dip, imposed upon the first broad bump
in spectrum. This intrinsic conductance dip originates from the superconductor state of the ring. When increasing the magnetic
flux from one quantum magnetic flux to two, the spectrum shifts toward higher energy region in the whole. This conductance
dip accordingly shifts and appears in the second bump. In the presence of a point-scatterer at the node, the spectrum is substantially
modified. Based on the condition of the formation of the standing wave functions in the ring and the broken of the time-reserve
symmetry of Schr?dinger equation after switching magnetic flux, the characteristics of transmission of electrons in this structure
can be well understood.
Received 6 November 2001 相似文献
976.
At the new high flux reactor FRM-II in Munich the accelerator MAFF (Munich accelerator for fission fragments) is under design.
In the high neutron flux of 1014 n/cm2 s up to 1014 neutron-rich fission fragments per second are produced in the 1 g U-235 target. Ions with an energy of 30 keV are extracted
from the ion source. In the mass separator two isotopes can be selected. One of the beams is used for low energy experiments,
the other one is injected into an ECRIS (or EBIS) for charge breeding to a q/A≥0.16. A gas filled RFQ cooler is used for emittance improvement. The subsequent LINAC delivers beams with an energy ranging
from 3.7 MeV/u to 5.9 MeV/u. New IH structures are being developed at the Munich tandem laboratory. A small storage ring is
planned in a further stage to recycle the fission fragments. A thin target foil can be placed into this ring, e.g., for synthesis
of super-heavy elements. The through-going beam tube has been installed in the heavy water tank of the reactor. Tests of the
target ion source in a special oven to test long term stability and safety tests were in progress. 相似文献
977.
Nikolai Neumaier 《Communications in Mathematical Physics》2002,230(2):271-288
In this paper we explicitly construct local ν-Euler derivations , where the ξα are local, conformally symplectic vector fields and the are formal series of locally defined differential operators, for Fedosov star products on a symplectic manifold (M,ω) by means of which we are able to compute Deligne's characteristic class of these star products. We show that this class
is given by , where is a formal series of closed two-forms on M the cohomology class of which coincides with the one introduced by Fedosov to classify his star products. Moreover, we consider
star products that have additional algebraic structures and compute the effect of these structures on the corresponding characteristic
classes of these star products. Specifying the constituents of Fedosov's construction we obtain star products with these special
properties. Finally, we investigate equivalence transformations between such special star products and prove existence of
equivalence transformations being compatible with the considered algebraic structures.
Dedicated to the memory of Moshé Flato
Received: 28 June 1999 / Accepted: 11 April 2002?Published online: 11 September 2002 相似文献
978.
A pressure sensitive paint (PSP) measurement has been known as a pressure field measurement technique based on the oxygen quenching phenomenon of luminescence of specific luminophores. A PSP measurement was applied for pressure field measurement in a low-solidity circular cascade diffuser of a single-stage transonic centrifugal compressor with 5 in pressure ratio for HFC134a gas. The oxygen concentration was about 500 ppm. Ru (bath-phen) was adsorbed on a silica-gel thinlayer chromatography sheet, and the sheet was pasted onto the side-wall between the cascade vanes. A drastic change in luminescent intensity was recognized during a surge condition. Also the pressure variations based on luminescent intensity agreed well with the pressure fluctuations measured using a semiconductor pressure sensor with high-frequency-response. It was shown that a PSP measurement worked well to investigate the unsteady pressure fields in a circular cascade diffuser of a transonic centrifugal compressor. Moreover, the time response of PSP becomes clear as a problem to be overcome for the present. 相似文献
979.
The production system using kanban was pioneered by Toyota Motor Company in Japan and subsequently it was adopted by numerous other Japanese and US companies for applying the just-in-time manufacturing principles. This research studies a single-stage supply chain system that is controlled by kanban mechanism. The supply chain system is modelled as a mixed-integer nonlinear programming (MINLP) problem. It is solved optimally by branch-and-bound method to determine the number of kanbans, batch size, number of batches, and the total quantity over one period. Meanwhile, the kanban operation between two adjacent plants is worked out considering the factors of loading and unloading time, and transport time. Coupled with plant-wide efforts for cost control and management commitment to enhance other measures of performance, a logistics system for controlling the production as well as the supply chain system is developed, which results in minimizing the total cost of the supply chain system. The results show that the improvements in reduction of inventory, wasted labour, and customer service in a supply chain are accomplished through the kanban mechanism. 相似文献
980.
Óscar Ciaurri 《Rendiconti del Circolo Matematico di Palermo》2004,53(2):231-234
A transference theorem for multipliers of Hermite expansions is proved. The result allows to transfer weightedL
2(ℝ
n
) estimates from lower to higher dimensions.
Research of the author supported by grant BFM2003-06335-603-03 of the D.G.I.. 相似文献