54 research outputs found
A gapless charge mode induced by the boundary states in the half-filled Hubbard open-chain
We discuss the ground state and some excited states of the half-filled
Hubbard model defined on an open chain with L sites, where only one of the
boundary sites has a different value of chemical potential. We consider the
case when the boundary site has a negative chemical potential -p and the
Hubbard coupling U is positive. By an analytic method we show that when p is
larger than the transfer integral some of the ground-state solutions of the
Bethe ansatz equations become complex-valued. It follows that there is a
``surface phase transition'' at some critical value p_c; when p<p_c all the
charge excitations have the gap for the half-filled band, while there exists a
massless charge mode when p>p_c.Comment: Revtex, 25 pages, 3 eps figures; Full revision with Appendixes adde
Doping and temperature dependence of electron spectrum and quasiparticle dispersion in doped bilayer cuprates
Within the t-t'-J model, the electron spectrum and quasiparticle dispersion
in doped bilayer cuprates in the normal state are discussed by considering the
bilayer interaction. It is shown that the bilayer interaction splits the
electron spectrum of doped bilayer cuprates into the bonding and antibonding
components around the point. The differentiation between the bonding
and antibonding components is essential, which leads to two main flat bands
around the point below the Fermi energy. In analogy to the doped
single layer cuprates, the lowest energy states in doped bilayer cuprates are
located at the point. Our results also show that the striking
behavior of the electronic structure in doped bilayer cuprates is intriguingly
related to the bilayer interaction together with strong coupling between the
electron quasiparticles and collective magnetic excitations.Comment: 9 pages, 4 figures, updated references, added figures and
discussions, accepted for publication in Phys. Rev.
Magnetic susceptibility and low-temperature specific-heat of integrable 1-D Hubbard model under open-boundary conditions
The magnetic susceptibility and the low-temperature specific heat of the
1-dimensional Hubbard model under the integrable open-boundary conditions are
discussed through the Bethe ansatz with the string hypothesis. The
contributions of the boundary fields to both the susceptibility and the
specific heat are obtained, and their exact expressions are analytically
derived.Comment: 14 pages, Latex, No figures, to appear in J. Phys. A: Gen. & Mat
Integrability of the Heisenberg Chains with Boundary Impurities and Their Bethe Ansatz
In this paper, we show the integrability of spin-1/2 XXZ Heisenberg chain
with two arbitrary spin boundary Impurities. By using the fusion method, we
generalize it to the spin-1 XXZ chain. Then the eigenvalues of Hamiltonians of
these models are obtained by the means of Bethe ansatz method.Comment: 13 pages, latex, no figures, to be appeared in J.Phys.
N-Cadherin Expression Level Distinguishes Reserved versus Primed States of Hematopoietic Stem Cells
SummaryOsteoblasts expressing the homophilic adhesion molecule N-cadherin form a hematopoietic stem cell (HSC) niche. Therefore, we examined how N-cadherin expression in HSCs relates to their function. We found that bone marrow (BM) cells highly expressing N-cadherin (N-cadherinhi) are not stem cells, being largely devoid of a Lineage−Sca1+cKit+ population and unable to reconstitute hematopoietic lineages in irradiated recipient mice. Instead, long-term HSCs form distinct populations expressing N-cadherin at intermediate (N-cadherinint) or low (N-cadherinlo) levels. The minority N-cadherinlo population can robustly reconstitute the hematopoietic system, express genes that may prime them to mobilize, and predominate among HSCs mobilized from BM to spleen. The larger N-cadherinint population performs poorly in reconstitution assays when freshly isolated but improves in response to overnight in vitro culture. Their expression profile and lower cell-cycle entry rate suggest N-cadherinint cells are being held in reserve. Thus, differential N-cadherin expression reflects functional distinctions between two HSC subpopulations
Limit Order Flow, Market Impact and Optimal Order Sizes: Evidence from NASDAQ TotalView-ITCH Data
Is the astronomical forcing a reliable and unique pacemaker for climate? A conceptual model study
There is evidence that ice age cycles are paced by astronomical forcing,
suggesting some kind of synchronisation phenomenon. Here, we identify the type
of such synchronisation and explore systematically its uniqueness and
robustness using a simple paleoclimate model akin to the van der Pol relaxation
oscillator and dynamical system theory. As the insolation is quite a complex
quasiperiodic signal involving different frequencies, the traditional concepts
used to define synchronisation to periodic forcing are no longer applicable.
Instead, we explore a different concept of generalised synchronisation in terms
of (coexisting) synchronised solutions for the forced system, their basins of
attraction and instabilities. We propose a clustering technique to compute the
number of synchronised solutions, each of which corresponds to a different
paleoclimate history. In this way, we uncover multistable synchronisation
(reminiscent of phase- or frequency-locking to individual periodic components
of astronomical forcing) at low forcing strength, and monostable or unique
synchronisation at stronger forcing. In the multistable regime, different
initial conditions may lead to different paleoclimate histories. To study their
robustness, we analyse Lyapunov exponents that quantify the rate of convergence
towards each synchronised solution (local stability), and basins of attraction
that indicate critical levels of external perturbations (global stability). We
find that even though synchronised solutions are stable on a long term, there
exist short episodes of desynchronisation where nearby climate trajectories
diverge temporarily (for about 50 kyr). (...)Comment: 22 pages, 18 figure
MLL2 Is Required in Oocytes for Bulk Histone 3 Lysine 4 Trimethylation and Transcriptional Silencing
Conditional knockout mouse strategies identify the histone methyltranferase MLL2 as a key player in epigenetic reprogramming of female gametes
Thermal environmental control of high-rise layer houses in California
The ventilation systems of two high-rise layer houses in California were monitored from 10/25/07 to 10/31/09 (m/d/y) for the National Air Emission Monitoring Study to facilitate the calculation of air pollutant emission rates. The ventilation systems, building structural design, feeding systems, and manure management practices of the houses were identical. Each house had approximately 32,500 laying hens in cages on the second floor (layer room) and was mechanically ventilated in cross-flow fashion with 12 sidewall single-speed exhaust fans on the first floor, consisting of two 91 cm fans and ten 122 cm fans. The fan rotational speeds, differential static pressure, temperature, relative humidity, and the evaporative misting system of each house and outside weather variables were continuously monitored. All 24 fans were evaluated with a portable fan tester three times during the two-year test. Fan airflow models were developed from in situ fan test data to calculate the fan airflow rates based on house differential static pressure and fan rotational speeds. The results showed that the fan performance factors of the 91 cm and 122 cm fans were 75% and 84% of the airflows, respectively, of new unused fans. The daily mean dry standard house ventilation rate averaged 47 m(3) s(-1) at dry standard conditions and ranged from 12 to 88 m(3) s(-1). The daily mean hen-specific ventilation rates averaged 5 m(3) h(-1) hen(-1) and ranged from 1.3 to 9.8 m(3) h(-1) hen(-1). Relative uncertainties of the hourly mean hen-specific ventilation rates averaged +/- 4.8% and ranged from +/- 2.9% to +/- 8.8%. The house differential static pressures ranged from -35 to -10 Pa 92% of the time. The layer room temperatures were controlled by adjusting the ventilation rate, which generally increased with ambient temperature. The evaporative misting system decreased the layer room temperature by up to 8 degrees C from the ambient, or barn inlet, air temperature while contributing to an increase of up to 3.8 g kg(-1) in the house humidity ratio relative to barn inlet conditions.Agricultural Air Research Counci
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