84 research outputs found
Paired state in an integrable spin-1 boson model
An exactly solvable model describing the low density limit of the spin-1
bosons in a one-dimensional optical lattice is proposed. The exact Bethe ansatz
solution shows that the low energy physics of this system is described by a
quantum liquid of spin singlet bound pairs. Motivated by the exact results, a
mean-field approach to the corresponding three-dimensional system is carried
out. Condensation of singlet pairs and coexistence with ordinary Bose-Einstein
condensation are predicted.Comment: 6 pages, 1 figure, Revised versio
Role of Particle Interactions in the Feshbach Conversion of Fermion Atoms to Bosonic Molecules
We investigate the Feshbach conversion of fermion atomic pairs to condensed
boson molecules with a microscopic model that accounts the repulsive
interactions among all the particles involved. We find that the conversion
efficiency is enhanced by the interaction between boson molecules while
suppressed by the interactions between fermion atoms and between atom and
molecule. In certain cases, the combined effect of these interactions leads to
a ceiling of less than 100% on the conversion efficiency even in the adiabatic
limit. Our model predicts a non-monotonic dependence of the efficiency on mean
atomic density. Our theory agrees well with recent experiments on Li and
K.Comment: 5 pages, 4 figure
Multicomponent Bright Solitons in F = 2 Spinor Bose-Einstein Condensates
We study soliton solutions for the Gross--Pitaevskii equation of the spinor
Bose--Einstein condensates with hyperfine spin F=2 in one-dimension. Analyses
are made in two ways: by assuming single-mode amplitudes and by generalizing
Hirota's direct method for multi-components. We obtain one-solitons of
single-peak type in the ferromagnetic, polar and cyclic states, respectively.
Moreover, twin-peak type solitons both in the ferromagnetic and the polar state
are found.Comment: 15 pages, 8 figure
Spin effects in Bose-Glass phases
We study the mechanism of formation of Bose glass (BG) phases in the spin-1
Bose Hubbard model when diagonal disorder is introduced. To this aim, we
analyze first the phase diagram in the zero-hopping limit, there disorder
induces superposition between Mott insulator (MI) phases with different filling
numbers. Then BG appears as a compressible but still insulating phase. The
phase diagram for finite hopping is also calculated with the Gutzwiller
approximation. The bosons' spin degree of freedom introduces another scattering
channel in the two-body interaction modifying the stability of MI regions with
respect to the action of disorder. This leads to some peculiar phenomena such
as the creation of BG of singlets, for very strong spin correlation, or the
disappearance of BG phase in some particular cases where fluctuations are not
able to mix different MI regions
Few-body physics with ultracold atomic and molecular systems in traps
Few-body physics has played a prominent role in atomic, molecular and nuclear
physics since the early days of quantum mechanics. It is now possible---thanks
to tremendous progress in cooling, trapping, and manipulating ultracold
samples---to experimentally study few-body phenomena in trapped atomic and
molecular systems with unprecedented control. This review summarizes recent
studies of few-body phenomena in trapped atomic and molecular gases, with an
emphasis on small trapped systems. We start by introducing the free-space
scattering properties and then investigate what happens when two particles,
bosons or fermions, are placed in an external confinement. Next, various
three-body systems are treated analytically in limiting cases. Our current
understanding of larger two-component Fermi systems and Bose systems is
reviewed, and connections with the corresponding bulk systems are established.
Lastly, future prospects and challenges are discussed. Throughout this review,
commonalities with other systems such as nuclei or quantum dots are
highlighted.Comment: review article to be published in Rep. Prog. Phys. (66 pages, 21
figures
Manin matrices and Talalaev's formula
We study special class of matrices with noncommutative entries and
demonstrate their various applications in integrable systems theory. They
appeared in Yu. Manin's works in 87-92 as linear homomorphisms between
polynomial rings; more explicitly they read: 1) elements in the same column
commute; 2) commutators of the cross terms are equal: (e.g. ). We claim
that such matrices behave almost as well as matrices with commutative elements.
Namely theorems of linear algebra (e.g., a natural definition of the
determinant, the Cayley-Hamilton theorem, the Newton identities and so on and
so forth) holds true for them.
On the other hand, we remark that such matrices are somewhat ubiquitous in
the theory of quantum integrability. For instance, Manin matrices (and their
q-analogs) include matrices satisfying the Yang-Baxter relation "RTT=TTR" and
the so--called Cartier-Foata matrices. Also, they enter Talalaev's
hep-th/0404153 remarkable formulas: ,
det(1-e^{-\p}T_{Yangian}(z)) for the "quantum spectral curve", etc. We show
that theorems of linear algebra, after being established for such matrices,
have various applications to quantum integrable systems and Lie algebras, e.g
in the construction of new generators in (and, in general,
in the construction of quantum conservation laws), in the
Knizhnik-Zamolodchikov equation, and in the problem of Wick ordering. We also
discuss applications to the separation of variables problem, new Capelli
identities and the Langlands correspondence.Comment: 40 pages, V2: exposition reorganized, some proofs added, misprints
e.g. in Newton id-s fixed, normal ordering convention turned to standard one,
refs. adde
Sframe: An Efficient System for Detailed DC Simulation of Bipolar Analog Integrated Circuits Using Continuation Methods
In this paper we describe an experimental system called sframe which is being incorporated into the design for manufacturability initiative at the Reading Works of AT&T Bell Laboratories. Our system is able to perform detailed and accurate DC analyses of integrated circuits containing several hundred transistors to be fabricated in a relatively complex junction isolated complementary technology
Vertical Heterophoria and Postural Control in Nonspecific Chronic Low Back Pain
The purpose of this study was to test postural control during quiet standing in
nonspecific chronic low back pain (LBP) subjects with vertical heterophoria (VH)
before and after cancellation of VH; also to compare with healthy subjects with,
and without VH. Fourteen subjects with LBP took part in this study. The postural
performance was measured through the center of pressure displacements with a
force platform while the subjects fixated on a target placed at either 40 or 200
cm, before and after VH cancellation with an appropriate prism. Their postural
performance was compared to that of 14 healthy subjects with VH and 12 without
VH (i.e. vertical orthophoria) studied previously in similar conditions. For LBP
subjects, cancellation of VH with a prism improved postural performance. With
respect to control subjects (with or without VH), the variance of speed of the
center of pressure was higher, suggesting more energy was needed to stabilize
their posture in quiet upright stance. Similarly to controls, LBP subjects
showed higher postural sway when they were looking at a target at a far distance
than at a close distance. The most important finding is that LBP subjects with
VH can improve their performance after prism-cancellation of their VH. We
suggest that VH reflects mild conflict between sensory and motor inputs involved
in postural control i.e. a non optimal integration of the various signals. This
could affect the performance of postural control and perhaps lead to pain.
Nonspecific chronic back pain may results from such prolonged conflict
Combined analgesics in (headache) pain therapy: shotgun approach or precise multi-target therapeutics?
<p>Abstract</p> <p>Background</p> <p>Pain in general and headache in particular are characterized by a change in activity in brain areas involved in pain processing. The therapeutic challenge is to identify drugs with molecular targets that restore the healthy state, resulting in meaningful pain relief or even freedom from pain. Different aspects of pain perception, i.e. sensory and affective components, also explain why there is not just one single target structure for therapeutic approaches to pain. A network of brain areas ("pain matrix") are involved in pain perception and pain control. This diversification of the pain system explains why a wide range of molecularly different substances can be used in the treatment of different pain states and why in recent years more and more studies have described a superior efficacy of a precise multi-target combination therapy compared to therapy with monotherapeutics.</p> <p>Discussion</p> <p>In this article, we discuss the available literature on the effects of several fixed-dose combinations in the treatment of headaches and discuss the evidence in support of the role of combination therapy in the pharmacotherapy of pain, particularly of headaches. The scientific rationale behind multi-target combinations is the therapeutic benefit that could not be achieved by the individual constituents and that the single substances of the combinations act together additively or even multiplicatively and cooperate to achieve a completeness of the desired therapeutic effect.</p> <p>As an example the fixesd-dose combination of acetylsalicylic acid (ASA), paracetamol (acetaminophen) and caffeine is reviewed in detail. The major advantage of using such a fixed combination is that the active ingredients act on different but distinct molecular targets and thus are able to act on more signalling cascades involved in pain than most single analgesics without adding more side effects to the therapy.</p> <p>Summary</p> <p>Multitarget therapeutics like combined analgesics broaden the array of therapeutic options, enable the completeness of the therapeutic effect, and allow doctors (and, in self-medication with OTC medications, the patients themselves) to customize treatment to the patient's specific needs. There is substantial clinical evidence that such a multi-component therapy is more effective than mono-component therapies.</p
Antidromic vasodilatation and the migraine mechanism
Despite the fact that an unprecedented series of new discoveries in neurochemistry, neuroimaging, genetics and clinical pharmacology accumulated over the last 20 years has significantly increased our current knowledge, the underlying mechanism of the migraine headache remains elusive. The present review article addresses, from early evidence that emerged at the end of the nineteenth century, the role of ‘antidromic vasodilatation’ as part of the more general phenomenon, currently defined as neurogenic inflammation, in the unique type of pain reported by patients suffering from migraine headaches. The present paper describes distinctive orthodromic and antidromic properties of a subset of somatosensory neurons, the vascular- and neurobiology of peptides contained in these neurons, and the clinical–pharmacological data obtained in recent investigations using provocation tests in experimental animals and human beings. Altogether, previous and recent data underscore that antidromic vasodilatation, originating from the activation of peptidergic somatosensory neurons, cannot yet be discarded as a major contributing mechanism of the throbbing head pain and hyperalgesia of migraine
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