986 research outputs found
Atom-by-Atom Substitution of Mn in GaAs and Visualization of their Hole-Mediated Interactions
The discovery of ferromagnetism in Mn doped GaAs [1] has ignited interest in
the development of semiconductor technologies based on electron spin and has
led to several proof-of-concept spintronic devices [2-4]. A major hurdle for
realistic applications of (Ga,Mn)As, or other dilute magnetic semiconductors,
remains their below room-temperature ferromagnetic transition temperature.
Enhancing ferromagnetism in semiconductors requires understanding the
mechanisms for interaction between magnetic dopants, such as Mn, and
identifying the circumstances in which ferromagnetic interactions are maximized
[5]. Here we report the use of a novel atom-by-atom substitution technique with
the scanning tunnelling microscope (STM) to perform the first controlled atomic
scale study of the interactions between isolated Mn acceptors mediated by the
electronic states of GaAs. High-resolution STM measurements are used to
visualize the GaAs electronic states that participate in the Mn-Mn interaction
and to quantify the interaction strengths as a function of relative position
and orientation. Our experimental findings, which can be explained using
tight-binding model calculations, reveal a strong dependence of ferromagnetic
interaction on crystallographic orientation. This anisotropic interaction can
potentially be exploited by growing oriented Ga1-xMnxAs structures to enhance
the ferromagnetic transition temperature beyond that achieved in randomly doped
samples. Our experimental methods also provide a realistic approach to create
precise arrangements of single spins as coupled quantum bits for memory or
information processing purposes
Strain-controlled criticality governs the nonlinear mechanics of fibre networks
Disordered fibrous networks are ubiquitous in nature as major structural
components of living cells and tissues. The mechanical stability of networks
generally depends on the degree of connectivity: only when the average number
of connections between nodes exceeds the isostatic threshold are networks
stable (Maxwell, J. C., Philosophical Magazine 27, 294 (1864)). Upon increasing
the connectivity through this point, such networks undergo a mechanical phase
transition from a floppy to a rigid phase. However, even sub-isostatic networks
become rigid when subjected to sufficiently large deformations. To study this
strain-controlled transition, we perform a combination of computational
modeling of fibre networks and experiments on networks of type I collagen
fibers, which are crucial for the integrity of biological tissues. We show
theoretically that the development of rigidity is characterized by a
strain-controlled continuous phase transition with signatures of criticality.
Our experiments demonstrate mechanical properties consistent with our model,
including the predicted critical exponents. We show that the nonlinear
mechanics of collagen networks can be quantitatively captured by the
predictions of scaling theory for the strain-controlled critical behavior over
a wide range of network concentrations and strains up to failure of the
material
On the effect of resonances in composite Higgs phenomenology
We consider a generic composite Higgs model based on the coset SO(5)/SO(4)
and study its phenomenology beyond the leading low-energy effective lagrangian
approximation. Our basic goal is to introduce in a controllable and simple way
the lowest-lying, possibly narrow, resonances that may exist is such models. We
do so by proposing a criterion that we call partial UV completion. We
characterize the simplest cases, corresponding respectively to a scalar in
either singlet or tensor representation of SO(4) and to vectors in the adjoint
of SO(4). We study the impact of these resonances on the signals associated to
high-energy vector boson scattering, pointing out for each resonance the
characteristic patterns of depletion and enhancement with respect to the
leading-order chiral lagrangian. En route we derive the O(p^4) general chiral
lagrangian and discuss its peculiar accidental and approximate symmetries.Comment: v3: a few typos corrected. Conclusions unchange
In-reach specialist nursing teams for residential care homes : uptake of services, impact on care provision and cost-effectiveness
Background: A joint NHS-Local Authority initiative in England designed to provide a dedicated nursing and physiotherapy in-reach team (IRT) to four residential care homes has been evaluated.The IRT supported 131 residents and maintained 15 'virtual' beds for specialist nursing in these care homes.
Methods: Data captured prospectively (July 2005 to June 2007) included: numbers of referrals; reason for referral; outcome (e.g. admission to IRT bed, short-term IRT support); length of stay in IRT; prevented hospital admissions; early hospital discharges; avoided nursing home transfers; and detection of unrecognised illnesses. An economic analysis was undertaken.
Results: 733 referrals were made during the 2 years (range 0.5 to 13.0 per resident per annum)resulting in a total of 6,528 visits. Two thirds of referrals aimed at maintaining the resident's independence in the care home. According to expert panel assessment, 197 hospital admissions were averted over the period; 20 early discharges facilitated; and 28 resident transfers to a nursing home prevented. Detection of previously unrecognised illnesses accounted for a high number of visits. Investment in IRT equalled £44.38 per resident per week. Savings through reduced hospital admissions, early discharges, delayed transfers to nursing homes, and identification of previously
unrecognised illnesses are conservatively estimated to produce a final reduction in care cost of £6.33 per resident per week. A sensitivity analysis indicates this figure might range from a weekly overall saving of £36.90 per resident to a 'worst case' estimate of £2.70 extra expenditure per resident per week.
Evaluation early in implementation may underestimate some cost-saving activities and greater savings may emerge over a longer time period. Similarly, IRT costs may reduce over time due to the potential for refinement of team without major loss in effectiveness.
Conclusion: Introduction of a specialist nursing in-reach team for residential homes is at least cost neutral and, in all probability, cost saving. Further benefits include development of new skills in the care home workforce and enhanced quality of care. Residents are enabled to stay in familiar surroundings rather than unnecessarily spending time in hospital or being transferred to a higher
dependency nursing home setting
Tuning supersymmetric models at the LHC: A comparative analysis at two-loop level
We provide a comparative study of the fine tuning amount (Delta) at the
two-loop leading log level in supersymmetric models commonly used in SUSY
searches at the LHC. These are the constrained MSSM (CMSSM), non-universal
Higgs masses models (NUHM1, NUHM2), non-universal gaugino masses model (NUGM)
and GUT related gaugino masses models (NUGMd). Two definitions of the fine
tuning are used, the first (Delta_{max}) measures maximal fine-tuning wrt
individual parameters while the second (Delta_q) adds their contribution in
"quadrature". As a direct result of two theoretical constraints (the EW minimum
conditions), fine tuning (Delta_q) emerges as a suppressing factor (effective
prior) of the averaged likelihood (under the priors), under the integral of the
global probability of measuring the data (Bayesian evidence p(D)). For each
model, there is little difference between Delta_q, Delta_{max} in the region
allowed by the data, with similar behaviour as functions of the Higgs, gluino,
stop mass or SUSY scale (m_{susy}=(m_{\tilde t_1} m_{\tilde t_2})^{1/2}) or
dark matter and g-2 constraints. The analysis has the advantage that by
replacing any of these mass scales or constraints by their latest bounds one
easily infers for each model the value of Delta_q, Delta_{max} or vice versa.
For all models, minimal fine tuning is achieved for M_{higgs} near 115 GeV with
a Delta_q\approx Delta_{max}\approx 10 to 100 depending on the model, and in
the CMSSM this is actually a global minimum. Due to a strong (
exponential) dependence of Delta on M_{higgs}, for a Higgs mass near 125 GeV,
the above values of Delta_q\approx Delta_{max} increase to between 500 and
1000. Possible corrections to these values are briefly discussed.Comment: 23 pages, 46 figures; references added; some clarifications (section
2
AHRQ series on complex intervention systematic reviews – paper 2: defining complexity, formulating scope, and questions
The early stages of a systematic review set the scope and expectations. This can be particularly challenging for complex interventions given their multidimensional and dynamic nature.
This paper builds on concepts introduced in paper 1 of this series. It describes the methodological, practical, and philosophical challenges and potential approaches for formulating the questions and scope of systematic reviews of complex interventions. Furthermore, it discusses the use of theory to help organize reviews of complex interventions.
Many interventions in medicine, public health, education, social services, behavioral health, and community programs are complex, and they may not fit neatly within the established paradigm for reviews of straightforward interventions. This paper provides conceptual and operational guidance for these early stages of scope formulation to assist authors of systematic reviews of complex interventions.This project was funded under Contract No. HHSA290201200004C from the Agency for Healthcare Research and Quality (AHRQ) , U.S. Department of Health and Human Services
Factors associated with preservation of facial nerve function after surgical resection of vestibular schwannoma
Avoidance of facial nerve palsy is one of the major goals of vestibular schwannoma (VS) microsurgery. In this study, we examined the significance of previously implicated prognostic factors (age, tumor size, the extent of resection and the surgical approach) on post-operative facial nerve function. We selected all VS patients from prospectively collected database (1984–2009) who underwent microsurgical resection as their initial treatment for histopathologically confirmed VS. The effect of variables such as surgical approach, tumor size, patient age and extent of resection on rates facial nerve dysfunction after surgery, were analyzed using multivariate logistic regression. Patients with preoperative facial nerve dysfunction (House-Brackman [HB] score 3 or higher) were excluded, and HB grade of 1 or 2 at the last follow-up visit was defined as “facial nerve preservation.” A total of 624 VS patients were included in this study. Multivariate logistic regression analysis found that only pre-operative tumor size significantly predicted poorer facial nerve outcome for patients followed-up for ≥6 and ≥12 months (OR 1.27, 95% CI 1.09–1.49, p < 0.01; OR 1.35, 95% CI 1.10–1.67, P < 0.01, respectively). We found no significant relationship between facial nerve function and age, extent of resection, surgical approach, or tumor size (when extent of resection and surgical approach were included in the regression analysis). Because facial nerve palsy is a debilitating and psychologically devastating condition for the patient, we suggest altering surgical aggressiveness in patients with unfavorable tumor anatomy, particularly in cases with large tumors where overaggressive resection might subject the patient to unwarranted risk. Residual disease can be followed and controlled with radiosurgery if interval growth is noted
A SM-like Higgs near 125 GeV in low energy SUSY: a comparative study for MSSM and NMSSM
Motivated by the recent LHC hints of a Higgs boson around 125 GeV, we assume
a SM-like Higgs with the mass 123-127 GeV and study its implication in low
energy SUSY by comparing the MSSM and NMSSM. We consider various experimental
constraints at 2-sigma level (including the muon g-2 and the dark matter relic
density) and perform a comprehensive scan over the parameter space of each
model. Then in the parameter space which is allowed by current experimental
constraints and also predicts a SM-like Higgs in 123-127 GeV, we examine the
properties of the sensitive parameters (like the top squark mass and the
trilinear coupling A_t) and calculate the rates of the di-photon signal and the
VV^* (V=W,Z) signals at the LHC. Our typical findings are: (i) In the MSSM the
top squark and A_t must be large and thus incur some fine-tuning, which can be
much ameliorated in the NMSSM; (ii) In the MSSM a light stau is needed to
enhance the di-photon rate of the SM-like Higgs to exceed its SM prediction,
while in the NMSSM the di-photon rate can be readily enhanced in several ways;
(iii) In the MSSM the signal rates of pp -> h -> VV^* at the LHC are never
enhanced compared with their SM predictions, while in the NMSSM they may get
enhanced significantly; (iv) A large part of the parameter space so far
survived will be soon covered by the expected XENON100(2012) sensitivity
(especially for the NMSSM).Comment: Version in JHEP (refs added
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