1,491 research outputs found
Theory for p-Wave Feshbach Molecules
We determine the physical properties of \emph{p}-wave Feshbach molecules in
doubly spin-polarized K and find excellent agreement with recent
experiments. We show that these molecules have a large probability to be in
the closed channel or bare molecular state responsible for the Feshbach
resonance. In the superfluid state this allows for observation of Rabi
oscillations between the molecular and atomic components of the Bose-Einstein
condensed pairs, which contains a characteristic signature of the quantum phase
transition that occurs as a function of applied magnetic field.Comment: Replaced with published versio
Sarma Phase in Trapped Unbalanced Fermi Gases
We consider a trapped unbalanced Fermi gas at nonzero temperatures where the
superfluid Sarma phase is stable. We determine in particular the phase
boundaries between the superfluid, normal, and phase separated regions of the
trapped unbalanced Fermi mixture. We show that the physics of the Sarma phase
is sufficient to understand the recent observations of Zwierlein et al.
[Science 311, 492 (2006); Nature 442, 54 (2006)] and indicate how the apparent
contradictions between this experiment and the experiment of Partridge et al.
[Science 311, 503 (2006)] may be resolved.Comment: Replaced with published version; 4 pages, 3 figure
Two ultracold atoms in a completely anisotropic trap
As a limiting case of ultracold atoms trapped in deep optical lattices, we
consider two interacting atoms trapped in a general anisotropic harmonic
oscillator potential, and obtain exact solutions of the Schrodinger equation
for this system. The energy spectra for different geometries of the trapping
potential are compared.Comment: 4 pages, 2 figure
Resonant Superfluidity in an Optical Lattice
We study a system of ultracold fermionic Potassium (40K) atoms in a
three-dimensional optical lattice in the vicinity of an s-wave Feshbach
resonance. Close to resonance, the system is described by a multi-band
Bose-Fermi Hubbard Hamiltonian. We derive an effective lowest-band Hamiltonian
in which the effect of the higher bands is incorporated by a self-consistent
mean-field approximation. The resulting model is solved by means of Generalized
Dynamical Mean-Field Theory. In addition to the BEC/BCS crossover we find a
phase transition to a fermionic Mott insulator at half filling, induced by the
repulsive fermionic background scattering length. We also calculate the
critical temperature of the BEC/BCS-state and find it to be minimal at
resonance.Comment: 19 pages, 3 figure
Renormalization Group Theory for the Imbalanced Fermi Gas
We formulate a wilsonian renormalization group theory for the imbalanced
Fermi gas. The theory is able to recover quantitatively well-established
results in both the weak-coupling and the strong-coupling (unitarity) limit. We
determine for the latter case the line of second-order phase transitions of the
imbalanced Fermi gas and in particular the location of the tricritical point.
We obtain good agreement with the recent experiments of Y. Shin {\it et al}.
[Nature {\bf 451}, 689 (2008)].Comment: Replaced with published versio
Dynamics of cold bosons in optical lattices: Effects of higher Bloch bands
The extended effective multiorbital Bose-Hubbard-type Hamiltonian which takes
into account higher Bloch bands, is discussed for boson systems in optical
lattices, with emphasis on dynamical properties, in relation with current
experiments. It is shown that the renormalization of Hamiltonian parameters
depends on the dimension of the problem studied. Therefore, mean field phase
diagrams do not scale with the coordination number of the lattice. The effect
of Hamiltonian parameters renormalization on the dynamics in reduced
one-dimensional optical lattice potential is analyzed. We study both the
quasi-adiabatic quench through the superfluid-Mott insulator transition and the
absorption spectroscopy, that is energy absorption rate when the lattice depth
is periodically modulated.Comment: 23 corrected interesting pages, no Higgs boson insid
Ground states and dynamics of population-imbalanced Fermi condensates in one dimension
By using the numerically exact density-matrix renormalization group (DMRG)
approach, we investigate the ground states of harmonically trapped
one-dimensional (1D) fermions with population imbalance and find that the
Larkin-Ovchinnikov (LO) state, which is a condensed state of fermion pairs with
nonzero center-of-mass momentum, is realized for a wide range of parameters.
The phase diagram comprising the two phases of i) an LO state at the trap
center and a balanced condensate at the periphery and ii) an LO state at the
trap center and a pure majority component at the periphery, is obtained. The
reduced two-body density matrix indicates that most of the minority atoms
contribute to the LO-type quasi-condensate. With the time-dependent DMRG, we
also investigate the real-time dynamics of a system of 1D fermions in response
to a spin-flip excitation.Comment: 20 pages, 15 figures, accepted for publication in New Journal of
Physic
Fussing About Fission: Defining Variety Among Mainstream and Exotic Apicomplexan Cell Division Modes
Cellular reproduction defines life, yet our textbook-level understanding of cell division is limited to a small number of model organisms centered around humans. The horizon on cell division variants is expanded here by advancing insights on the fascinating cell division modes found in the Apicomplexa, a key group of protozoan parasites. The Apicomplexa display remarkable variation in offspring number, whether karyokinesis follows each S/M-phase or not, and whether daughter cells bud in the cytoplasm or bud from the cortex. We find that the terminology used to describe the various manifestations of asexual apicomplexan cell division emphasizes either the number of offspring or site of budding, which are not directly comparable features and has led to confusion in the literature. Division modes have been primarily studied in two human pathogenic Apicomplexa, malaria-causing Plasmodium spp. and Toxoplasma gondii, a major cause of opportunistic infections. Plasmodium spp. divide asexually by schizogony, producing multiple daughters per division round through a cortical budding process, though at several life-cycle nuclear amplifications stages, are not followed by karyokinesis. T. gondii divides by endodyogeny producing two internally budding daughters per division round. Here we add to this diversity in replication mechanisms by considering the cattle parasite Babesia bigemina and the pig parasite Cystoisospora suis. B. bigemina produces two daughters per division round by a βbinary fissionβ mechanism whereas C. suis produces daughters through both endodyogeny and multiple internal budding known as endopolygeny. In addition, we provide new data from the causative agent of equine protozoal myeloencephalitis (EPM), Sarcocystis neurona, which also undergoes endopolygeny but differs from C. suis by maintaining a single multiploid nucleus. Overall, we operationally define two principally different division modes: internal budding found in cyst-forming Coccidia (comprising endodyogeny and two forms of endopolygeny) and external budding found in the other parasites studied (comprising the two forms of schizogony, binary fission and multiple fission). Progressive insights into the principles defining the molecular and cellular requirements for internal vs. external budding, as well as variations encountered in sexual stages are discussed. The evolutionary pressures and mechanisms underlying apicomplexan cell division diversification carries relevance across Eukaryota
Biogenesis of the inner membrane complex is dependent on vesicular transport by the alveolate specific GTPase Rab11B
Apicomplexan parasites belong to a recently recognised group of protozoa referred to as Alveolata. These protists contain membranous sacs (alveoli) beneath the plasma membrane, termed the Inner Membrane Complex (IMC) in the case of Apicomplexa. During parasite replication the IMC is formed de novo within the mother cell in a process described as internal budding. We hypothesized that an alveolate specific factor is involved in the specific transport of vesicles from the Golgi to the IMC and identified the small GTPase Rab11B as an alveolate specific Rab-GTPase that localises to the growing end of the IMC during replication of Toxoplasma gondii. Conditional interference with Rab11B function leads to a profound defect in IMC biogenesis, indicating that Rab11B is required for the transport of Golgi derived vesicles to the nascent IMC of the daughter cell. Curiously, a block in IMC biogenesis did not affect formation of sub-pellicular microtubules, indicating that IMC biogenesis and formation of sub-pellicular microtubules is not mechanistically linked. We propose a model where Rab11B specifically transports vesicles derived from the Golgi to the immature IMC of the growing daughter parasites
A Novel Family of Toxoplasma IMC Proteins Displays a Hierarchical Organization and Functions in Coordinating Parasite Division
Apicomplexans employ a peripheral membrane system called the inner membrane complex (IMC) for critical processes such as host cell invasion and daughter cell formation. We have identified a family of proteins that define novel sub-compartments of the Toxoplasma gondii IMC. These IMC Sub-compartment Proteins, ISP1, 2 and 3, are conserved throughout the Apicomplexa, but do not appear to be present outside the phylum. ISP1 localizes to the apical cap portion of the IMC, while ISP2 localizes to a central IMC region and ISP3 localizes to a central plus basal region of the complex. Targeting of all three ISPs is dependent upon N-terminal residues predicted for coordinated myristoylation and palmitoylation. Surprisingly, we show that disruption of ISP1 results in a dramatic relocalization of ISP2 and ISP3 to the apical cap. Although the N-terminal region of ISP1 is necessary and sufficient for apical cap targeting, exclusion of other family members requires the remaining C-terminal region of the protein. This gate-keeping function of ISP1 reveals an unprecedented mechanism of interactive and hierarchical targeting of proteins to establish these unique sub-compartments in the Toxoplasma IMC. Finally, we show that loss of ISP2 results in severe defects in daughter cell formation during endodyogeny, indicating a role for the ISP proteins in coordinating this unique process of Toxoplasma replication
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