Non-linear response to electric field in extended Hubbard models

The electric-field response of a one-dimensional ring of interacting fermions, where the interactions are described by the extended Hubbard model, is investigated. By using an accurate real-time propagation scheme based on the Chebyshev expansion of the evolution operator, we uncover various non-linear regimes for a range of interaction parameters that allows modeling of metallic and insulating (either charge density wave or spin density wave insulators) rings. The metallic regime appears at the phase boundary between the two insulating phases and provides the opportunity to describe either weakly or strongly correlated metals. We find that the {\it fidelity susceptibility} of the ground state as a function of magnetic flux piercing the ring provides a very good measure of the short-time response. Even completely different interacting regimes behave in a similar manner at short time-scales as long as the fidelity susceptibility is the same. Depending on the strength of the electric field we find various types of responses: persistent currents in the insulating regime, dissipative regime or damped Bloch-like oscillations with varying frequencies or even irregular in nature. Furthermore, we also consider the dimerization of the ring and describe the response of a correlated band insulator. In this case the distribution of the energy levels is more clustered and the Bloch-like oscillations become even more irregular

Field effect on surface states in a doped Mott-Insulator thin film

Surface effects of a doped thin film made of a strongly correlated material are investigated both in the absence and presence of a perpendicular electric field. We use an inhomogeneous Gutzwiller approximation for a single band Hubbard model in order to describe correlation effects. For low doping, the bulk value of the quasiparticle weight is recovered exponentially deep into the slab, but with increasing doping, additional Friedel oscillations appear near the surface. We show that the inverse correlation length has a power-law dependence on the doping level. In the presence of an electrical field, considerable changes in the quasiparticle weight can be realized throughout the system. We observe a large difference (as large as five orders of magnitude) in the quasiparticle weight near the opposite sides of the slab. This effect can be significant in switching devices that use the surface states for transport

The buffalo wars

Thesis (S.M. in Science Writing)--Massachusetts Institute of Technology, Dept. of Humanities, Graduate Program in Science Writing, 2006."September 2006."Includes bibliographical references (leaves 38-42).The wandering buffalo of Yellowstone National Park are the subject of a heated debate in the western United States. The animals carry a disease called brucellosis, which infects both buffalo and cattle and has economic consequences for ranchers. Some ranchers fear that buffalo, as they migrate out of Yellowstone in search of forage, will transmit the disease to cattle around the park and jeopardize their financial well-being. The Park Service and other government agencies have tried to control the situation by exercising a lethal form of boundary control for buffalo, though other wildlife species are unregulated. Animal advocates dispute the agencies' tactics. Native Americans wonder why the buffalo are entirely under agency control. The park has become somewhat of a war zone, where the groups quarrel throughout the migratory season. Their disagreement is about much more than the animals themselves, taking root in even older and deeper conflicts. Yet despite the tangled nature of the problem, there may be room for negotiation and eventual resolution.by Susan L. Nasr.S.M.in Science Writin

Overcoming barriers to a successful transition from pediatric to adult care

As life expectancy for people with cystic fibrosis (CF) has increased dramatically, so has the need for a guided, structured transition from pediatric to adult-focused care. A formalized transition program allows for seamless transfer of patients between providers, helping to ensure continuity of care, and avoid potential declines associated with inconsistent medical care. New CF Center guidelines issued by the CFF strongly recommend that each center establish a transition program for age-appropriate transition to an adult CF clinic. In this article, we explore the remaining barriers to establishing a transition program in a CF Center and offer examples of several successful models. We describe CFF-sponsored and other initiatives that exist to support centers in establishing a transition program and discuss the need for ongoing research in this area

Who Counsels Parents of Newborns Who Are Carriers of Sickle Cell Anemia or Cystic Fibrosis?

Our objective was to describe: 1) physicians’ knowledge of whether genetic counseling is provided to parents of newborns with sickle cell trait (SCT) or who are cystic fibrosis carriers (CFC), and 2) the prevalence of genetic counseling provided by primary care physicians. We conducted a cross‐sectional descriptive survey of 600 randomly‐sampled Michigan‐based pediatricians and family physicians, assessing physician knowledge of where and whether genetic counseling is received by parents whose newborns are carriers. Chi‐squared testing determined associations between genetic counseling location and physician demographic characteristics. Our response rate was 62 %: 298 (84 %) provided infant well care (183 pediatricians, 115 family physicians). Most respondents were non‐Hispanic White (65 %). Virtually all physicians believed parents whose newborns are carriers of either SCT or CFC should receive some genetic counseling (from the physician and/or another source), yet 20 % reported that parents of newborns with SCT did not receive counseling. Parents of infants with CFC received more counseling overall (92 % vs. 80 %; p < 0.01) and were counseled more frequently by genetic counselors or specialty centers than parents of newborns with SCT (85 % vs. 60 %; p < 0.01). Although physicians agreed that parents whose newborns are carriers should receive genetic counseling, fewer parents of newborns with SCT than with CFC received counseling from any source. This finding strongly suggests the need for further education and investigation of this apparent health disparity.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147004/1/jgc40218.pd

Spin Fidelity for Three-qubit Greenberger-Horne-Zeilinger and W States Under Lorentz Transformations

Constructing the reduced density matrix for a system of three massive spin$-\frac{1}{2}$ particles described by a wave packet with Gaussian momentum distribution and a spin part in the form of GHZ or W state, the fidelity for the spin part of the system is investigated from the viewpoint of moving observers in the jargon of special relativity. Using a numerical approach, it turns out that by increasing the boost speed, the spin fidelity decreases and reaches to a non-zero asymptotic value that depends on the momentum distribution and the amount of momentum entanglement.Comment: 12pages, 2 figure

Constructions and bounds for codes with restricted overlaps

Non-overlapping codes have been studied for almost 60 years. In such a code, no proper, non-empty prefix of any codeword is a suffix of any codeword. In this paper, we study codes in which overlaps of certain specified sizes are forbidden. We prove some general bounds and we give several constructions in the case of binary codes. Our techniques also allow us to provide an alternative, elementary proof of a lower bound on non-overlapping codes due to Levenshtein in 1964.Comment: 25 pages. Extra citations, typos corrected and explanations expande

Electrical field induced shift of the Mott Metal-Insulator transition in thin films

The ground state properties of a paramagnetic Mott insulator are investigated in the presence of an external electrical field using the inhomogeneous Gutzwiller approximation for a single band Hubbard model in a slab geometry. The metal insulator transition is shifted towards higher Hubbard repulsions by applying an electric field perpendicular to the slab. The spatial distribution of site dependent quasiparticle weight shows that the quasiparticle weight is maximum in few layers beneath the surface. Moreover only at higher Hubbard repulsion, larger than the bulk critical U, the electric field will be totally screened only for centeral cites. Our results show that by presence of an electric field perpendicular to a thin film made of a strongly correlated material, states near the surface will remain metallic while the bulk becomes insulating after some critical U. In contrast, in the absence of the electric field the surface becomes insulating before the bulk