Entanglement and spin squeezing in the two-atom Dicke model

We analyse the relation between the entanglement and spin-squeezing parameter in the two-atom Dicke model and identify the source of the discrepancy recently reported by Banerjee (2001 Preprint quant-ph/0110032) and Zhou et al (2002 J. Opt. B. Quantum Semiclass. Opt. 4 425), namely that one can observe entanglement without spin squeezing. Our calculations demonstrate that there are two criteria for entanglement, one associated with the two-photon coherences that create two-photon entangled states, and the other associated with populations of the collective states. We find that the spin-squeezing parameter correctly predicts entanglement in the two-atom Dicke system only if it is associated with two-photon entangled states, but fails to predict entanglement when it is associated with the entangled symmetric state. This explicitly identifies the source of the discrepancy and explains why the system can be entangled without spin squeezing. We illustrate these findings with three examples of the interaction of the system with thermal, classical squeezed vacuum, and quantum squeezed vacuum fields.

Dynamics of motor nerve terminal remodeling unveiled using SNARE-cleaving botulinum toxins: the extent and duration are dictated by the sites of SNAP-25 truncation

Nerve sprouts emerge from motor nerve terminals following blockade of exo-endocytosis for more than 3 days by botulinum neurotoxin (BoNT), and form functional synapses, albeit temporary. Upon restoration of synaptic activity to the parent terminal 7 and 90 days after exposure to BoNT/F or A respectively, a concomitant retraction of the outgrowths was observed. BoNT/E caused short-term neuroparalysis, and dramatically accelerated the recovery of BoNT/A-paralyzed muscle by further truncation of SNAP-25 and its replenishment with functional full-length SNARE. The removal of 9 C-terminal residues from SNAP-25 by BoNT/A leads to persistence of the inhibitory product due to the formation of a nonproductive SNARE complex(es) at release sites, whereas deletion of a further 17 amino acids permits replenishment and a speedy recovery. (C) 2003 Elsevier Science (USA). All rights reserved.

Spin squeezing as a measure of entanglement in a two-qubit system

We show that the two definitions of spin squeezing extensively used in the literature [M. Kitagawa and M. Ueda, Phys. Rev. A 47, 5138 (1993) and D.J. Wineland , Phys. Rev. A 50, 67 (1994)] give different predictions of entanglement in the two-atom Dicke system. We analyze differences between the definitions and show that the spin squeezing parameter of Kitagawa and Ueda is a better measure of entanglement than the commonly used spectroscopic spin squeezing parameter. We illustrate this relation by examining different examples of a driven two-atom Dicke system in which spin squeezing and entanglement arise dynamically. We give an explanation of the source of the difference using the negativity criterion for entanglement.

Entanglement of two atoms

We discuss the problem of creation of entangled states in a system of two two-level atoms which are separated by an arbitrary distance r(12) and interact with each other via the dipole-dipole interaction and both are driven by a laser field. The entangled antisymmetric state of the system is included throughout, even for small inter-atomic separations. Different mechanisms leading to effective transfer of population to the antisymmetric state are identified. The steady-state values of concurrence which is a measure of entanglement are calculated showing that perfect entanglement can be reached in case of two non-identical atoms.

Cerebellar language and cognitive functions in childhood: A comparative review of the clinical research

Background: Recent research addressing evidence from functional neuroimaging studies, neurophysiological research, and new advances in neuropsychology together with traditional cerebellar lesion studies have recently implicated the cerebellum in adult language and cognitive functions. However, more limited information is currently available in describing the functional connectivity present in the paediatric population. Aims: It is the purpose of this paper to review recent clinical research pertaining to paediatric populations, outlining the impact of site of lesion and specific associated clinical changes in children with cerebellar disturbances. Main contribution: The specific contribution of the right cerebellar hemisphere to language function is identified to also exist in the paediatric population, highlighting the existence of functional connections between this region of the brain and left frontal cortical areas early in development. Conclusions: Implications for future research in paediatric populations are extensive, as a greater awareness and an understanding of the recently acknowledged involvement of the cerebellum in cognition and nonmotor linguistic function is anticipated to also add new dimension and direction to the analysis of childhood language outcomes associated with the cerebellum.

Difficult macrocyclizations: New strategies for synthesizing highly strained cyclic tetrapeptides

Cyclic tetrapeptides are an intriguing class of natural products. To synthesize highly strained cyclic tetrapeptides; we developed a macrocyclization strategy that involves the inclusion of 2-hydroxy-6-nitrobenzyl (HnB) group at the N-terminus and in the middle of the sequence. The N-terminal auxiliary performs a ring closure/ring contraction role, and the backbone auxiliary promotes cis amide bonds to facilitate the otherwise difficult ring contraction. Following this route, the all-L cyclic tetrapeptide cyclo-[Tyr-Arg-Phe-Ala] was successfully prepared.

Advanced precursors in marine biosynthetic study. Part 3: The biosynthesis of dichloroimines in the tropical marine sponge Stylotella aurantium

The biosynthetic origins of the dichloroimine group in the stylotellanes A and B 1,2 have been investigated by incorporation of [C-14]-labeled farnesyl isocyanide 7 and farnesyl isothiocyanate 3 into the sponge Stylotella aurantium. (C) 2002 Elsevier Science Ltd. All rights reserled.

Comparative pharmacokinetics of metronidazole in camels, sheep and goats

The pharmacokinetics of metronidazole was determined after a single intramuscular (i.m.) dose of 30 mg.kg(-1)-body weight in five camels, sheep and goats. Marked differences were found between the three species in some of the kinetic parameters. For example, the elimination half-lives t(1/2); (h) in camels, sheep and goats were 10.0, 6.21 and 5.87, respectively. The drug maximum concentrations in plasma, C-max (mg.ml(-1)), were 28.3, 54.6 and 54.4 in camels, sheep and goats, respectively. The time to reach C-max, t(max) (h), were 5, 4 and 2 in camels, sheep and goats, respectively. The mean residence times (MRT; h) in camels, sheep and goats were 16.7, 10.8 and 8.64, respectively. In the light of the present kinetic data and known microbial sensitivities of metronidazole, we recommend an i.m. dose of 15 mg.kg(-1) in camels and 10 mg.kg(-1) in sheep and boats. every 12 h.