49 research outputs found
Quantum Entanglement in Second-quantized Condensed Matter Systems
The entanglement between occupation-numbers of different single particle
basis states depends on coupling between different single particle basis states
in the second-quantized Hamiltonian. Thus in principle, interaction is not
necessary for occupation-number entanglement to appear. However, in order to
characterize quantum correlation caused by interaction, we use the eigenstates
of the single-particle Hamiltonian as the single particle basis upon which the
occupation-number entanglement is defined. Using the proper single particle
basis, we discuss occupation-number entanglement in important eigenstates,
especially ground states, of systems of many identical particles. The
discussions on Fermi systems start with Fermi gas, Hatree-Fock approximation,
and the electron-hole entanglement in excitations. The entanglement in a
quantum Hall state is quantified as -fln f-(1-f)ln(1-f), where f is the proper
fractional part of the filling factor. For BCS superconductivity, the
entanglement is a function of the relative momentum wavefunction of the Cooper
pair, and is thus directly related to the superconducting energy gap. For a
spinless Bose system, entanglement does not appear in the
Hatree-Gross-Pitaevskii approximation, but becomes important in the Bogoliubov
theory.Comment: 11 pages. Journal versio
Istraživanja 3,4-diaril-1,2,5-oksadiazola i njihovih N-oksida: Potraga za boljim COX-2 inhibitorima
A series of 3,4-diaryl-1,2,5-oxadiazoles and 3,4-diaryl-1,2,5-oxadiazole N-oxides were prepared and evaluated for COX-2 and COX-1 binding affinity in vitro and for anti-inflammatory activity by the rat paw edema method. p-Methoxy (p-OMe) substituted compounds 9, 21, 34, 41, 42 showed COX-2 enzyme inhibition higher than that showed by compounds with other substituents. 3,4-Di(4-methoxyphenyl)-1,2,5-oxadiazole N-oxide (42) showed COX-2 enzyme inhibition of 54% at 22 µmol L-1 and COX-1 enzyme inhibition of 44% at 88 µmol L-1 concentrations, but showed very low in vivo anti-inflammatory activity. Its deoxygenated derivative (21) showed lower COX-2 enzyme inhibition (26% at 22 µmol L-1) and higher COX-1 enzyme inhibition (53% at 88 µmol L-1) but marked in vivo anti-inflammatory activity (71% at 25 mg kg-1) vs. celecoxib (48% at 12.5 mg kg-1). Molecular modeling (docking) studies showed that the methoxy group is positioned in the vicinity of the COX-2 secondary pocket and it also participates in hydrogen bonding interactions in the COX-2 active site. These preliminary studies suggest that the p-methoxy (p-OMe) group in one of benzene rings may give potentially active leads in this series of oxadiazole/N-oxides.Sintetizirana je serija 3,4-diaril-1,2,5-oksadiazola i 3,4-diaril-1,2,5-oksadiazol N-oksida i ocijenjena njihova sposobnost vezivanja na COX-2 i COX-1 in vitro i protuupalno djelovanje na edem šape štakora. Spojevi sa p-metoksi (p-OMe) supstituentom 9, 21, 34, 41, 42 bolje su inhibirali COX-2 nego ostali spojevi. 3,4-Di(4-metoksifenil)-1,2,5-oksadiazol N-oksid (42) inhibirao je COX-2 za 54% u koncentraciji od 22 µmol L-1, a COX-1 za 44% u koncentraciji 88 µmol L-1, ali je in vivo slabo djelovao protuupalno. Njegov deoksigenirani derivat 21 pokazao je slabiju inhibiciju COX-2 enzima (26% u koncentraciji 22 µmol L-1) i jaču inhibiciju COX-1 (71% u koncentraciji 25 mg kg-1) što je bolje od standarda celekoksiba (48% u koncentraciji 12,5 mg kg-1). Molekularno je modeliranje pokazalo da je metoksi skupina smještena u blizini sekundarnog džepa na enzimu COX-2 i da utječe na vodikove veze interakcija na aktivnom mjestu COX-2. Ova preliminarna istraživanja sugeriraju da bi se u seriji oksadiazol/N-oksida mogao naći predvodni spoj s p-metoksi skupinom na benzenskom prstenu
New varying speed of light theories
We review recent work on the possibility of a varying speed of light (VSL).
We start by discussing the physical meaning of a varying , dispelling the
myth that the constancy of is a matter of logical consistency. We then
summarize the main VSL mechanisms proposed so far: hard breaking of Lorentz
invariance; bimetric theories (where the speeds of gravity and light are not
the same); locally Lorentz invariant VSL theories; theories exhibiting a color
dependent speed of light; varying induced by extra dimensions (e.g. in the
brane-world scenario); and field theories where VSL results from vacuum
polarization or CPT violation. We show how VSL scenarios may solve the
cosmological problems usually tackled by inflation, and also how they may
produce a scale-invariant spectrum of Gaussian fluctuations, capable of
explaining the WMAP data. We then review the connection between VSL and
theories of quantum gravity, showing how ``doubly special'' relativity has
emerged as a VSL effective model of quantum space-time, with observational
implications for ultra high energy cosmic rays and gamma ray bursts. Some
recent work on the physics of ``black'' holes and other compact objects in VSL
theories is also described, highlighting phenomena associated with spatial (as
opposed to temporal) variations in . Finally we describe the observational
status of the theory. The evidence is currently slim -- redshift dependence in
the atomic fine structure, anomalies with ultra high energy cosmic rays, and
(to a much lesser extent) the acceleration of the universe and the WMAP data.
The constraints (e.g. those arising from nucleosynthesis or geological bounds)
are tight, but not insurmountable. We conclude with the observational
predictions of the theory, and the prospects for its refutation or vindication.Comment: Final versio