3,062 research outputs found
Physics case of the very high energy electron--proton collider, VHEeP
The possibility of a very high energy electron-proton (VHEeP) collider with a
centre-of-mass energy of 9 TeV has been presented at previous workshops. These
proceedings briefly summarise the VHEeP concept, which was recently published,
and developments since then, as well as future directions. At the VHEeP
collider, with a centre-of-mass energy 30 times greater than HERA, parton
momentum fractions, , down to about are accessible for photon
virtualities, , of 1 GeV. This extension in the kinematic range to low
complements proposals for other electron-proton or electron-ion colliders.Comment: 6 pages, 2 figures, for proceedings of DIS 2017 worksho
Coexistence of pressure-induced structural phases in bulk black phosphorus: a combined x-ray diffraction and Raman study up to 18 GPa
We report a study of the structural phase transitions induced by pressure in
bulk black phosphorus by using both synchrotron x-ray diffraction for pressures
up to 12.2 GPa and Raman spectroscopy up to 18.2 GPa. Very recently black
phosphorus attracted large attention because of the unique properties of
fewlayers samples (phosphorene), but some basic questions are still open in the
case of the bulk system. As concerning the presence of a Raman spectrum above
10 GPa, which should not be observed in an elemental simple cubic system, we
propose a new explanation by attributing a key role to the non-hydrostatic
conditions occurring in Raman experiments. Finally, a combined analysis of
Raman and XRD data allowed us to obtain quantitative information on presence
and extent of coexistences between different structural phases from ~5 up to
~15 GPa. This information can have an important role in theoretical studies on
pressure-induced structural and electronic phase transitions in black
phosphorus
Kidney Disease and Cognitive Function
We provide a brief review of research on chronic kidney disease and cognitive performance, including dementia. We touch briefly on the literature relating end-stage-renal disease to cognitive function, but focus on studies of modest and moderate forms of chronic kidney disease (CKD) that precede dialysis and transplantation. We summarize previous reviews dealing with case control studies of patients but more fully examine community-based studies with large samples and necessary controls for demographic risk factors, cardiovascular variables, and other confounds such as depression. In addition we suggest potential biological and social-psychological mediators between CKD and cognition. Studies follow in two categories of design: (1) cross-sectional studies; (2) longitudinal studies. In each, CKD is related to a wide range of deficits in cognitive functioning including, verbal and visual-memory and organization, and components of executive functioning and fluid intellect. In general, prior to the need to treat with hemodialysis (HD) or kidney transplant (KT), magnitude of effect with relation to CKD and function are small or modest in persons free from acute stroke and dementia. However, HD and KT can result in major impairment. We discuss needed controls, the greater demand on controls after HD and KT begin, and suggest that mechanisms intervening relations between hypertension, or diabetes, and cognitive performance may be similar to those intervening between hypertension and cognitive performance and the hypertension and diabetes literature on cognition provides a good model for the study of early stage kidney disease and cognitive ability. We posit that the mechanisms linking CKD and cognition may be similar to those linking hypertension or diabetes to cognition. We identify the need for more studies with multiple cognitive test batteries, measures of every-day cognitive abilities relevant to patient understanding of the disease and treatments, and more studies with prevalent and incident dementia outcomes
Rehabilitation following surgery for lumbar spinal stenosis: a Cochrane review
Study Design
A systematic review of randomised controlled trials (RCTs)
Objective
To determine the effects of active rehabilitation on functional outcome following lumbar spinal stenosis surgery when compared with 'usual postoperative care'.
Summary of background data
Surgery rates for lumbar spinal stenosis have risen, yet outcomes remain suboptimal. Post-operative rehabilitation has been suggested as a tool to improve post-operative function but, to date, there is limited evidence to support its use.
Methods
CENTRAL (The Cochrane Library), the Cochrane Back Review Group Trials Register, MEDLINE, EMBASE, CINAHL and PEDro electronic databases were searched. Randomised controlled trials (RCTs) comparing the effectiveness of active rehabilitation with usual care in adults with lumbar spinal stenosis who had undergone primary spinal decompression surgery were included. Two authors independently selected studies, assessed the risk of bias, and extracted the data in line with the recommendations of the Cochrane Back Review Group. Study results were pooled in a meta-analysis when appropriate using functional status as the primary outcome, with secondary outcomes including measures of leg pain, low back pain, and global improvement/general health. The GRADE approach was used to assess the quality of the evidence.
Results
Our searches yielded 1,726 articles, of which three studies (N = 373 participants) were suitable for inclusion in meta-analysis. All included studies were deemed to have low risk of bias; no study had unacceptably high dropout rates. There was moderate evidence suggesting that active rehabilitation was more effective than usual care in improving both short- and long-term functional status following surgery. Similar findings were noted for secondary outcomes, including short-term improvement in low back pain and long-term improvement in both low back pain and leg pain.
Conclusions
We obtained moderate-quality evidence indicating that postoperative active rehabilitation after decompression surgery for lumbar spinal stenosis is more effective than usual care. Further work is required particularly with respect to the cost effectiveness of such interventions
Hypertension and Cognitive Functioning: A Perspective in Historical Context
Our objective is to characterize the development of the literature on hypertension and cognitive functioning from a historical perspective. This goal was stimulated by the review on “Historical Trends and Milestones in Hypertension Research” in the October 2012 issue of Hypertension. Our specific aims are threefold: (1) to trace and describe the history of this area of research; (2) to identify milestones in knowledge and methods; and (3) to discuss briefly how this literature translates into patient care. The topic is of major relevance to research and practice because hypertension is a well-known risk factor for decline in cognitive performance within the normal range of cognitive functioning, mild cognitive impairment (MCI) and dementia. It is important to emphasize 3 features of the review: (1) it is not designed as a critical review of the literature, but rather to describe the historical influences on our current knowledge base (poor, mediocre and outstanding papers from the past have all shaped our present); (2) word-count limitations require that we omit statistical detail except to emphasize effect sizes in pivotal papers; and (3) each milestone topic is addressed by noting the earliest work then followed by examples of papers representing pivotal events. A number of comprehensive re- views of this literature are available, including a seminal paper summarizing the formative years of this research. Please see http://hyper.ahajournals.org for citations to additional reviews of the literature and papers published in Hypertension. We recognize the importance of the emerging literature on hypotension and cognitive function, but refer the readers to previous reviews which include this topic
Pressure-tuning of the electron-phonon coupling: the insulator to metal transition in manganites
A comprehensive understanding of the physical origin of the unique magnetic
and transport properties of A_(1-x)A'^xMnO_3 manganites (A = trivalent
rare-earth and A' = divalent alkali-earth metal) is still far from being
achieved. The complexity of these systems arises from the interplay among
several competing interactions of comparable strength. Recently the
electron-phonon coupling, triggered by a Jahn-Teller distortion of the MnO_6
octahedra, has been recognised to play an essential role in the insulator to
metal transition and in the closely related colossal magneto-resistance. The
pressure tuning of the octahedral distortion gives a unique possibility to
separate the basic interactions and, at least in principle, to follow the
progressive transformation of a manganite from an intermediate towards a weak
electron-phonon coupling regime. Using a diamond anvil cell, temperature and
pressure-dependent infrared absorption spectra of La_(0.75)Ca_(0.25)MnO_3 have
been collected and, from the spectral weight analysis, the pressure dependence
of the insulator to metal transition temperature T_IM has been determined for
the first time up to 11.2 GPa. The T_IM(P) curve we proposed to model the
present data revealed a universality character in accounting for the whole
class of intermediate coupling compounds. This property can be exploited to
distinguish the intermediate from the weak coupling compounds pointing out the
fundamental differences between the two coupling regimes.Comment: 8 pages, 4 figure
Electrodynamics of superconducting pnictide superlattices
It has been recently reported (S. Lee et al., Nature Materials 12, 392, 2013)
that superlattices where layers of the 8% Co-doped BaFe2As2 superconducting
pnictide are intercalated with non superconducting ultrathin layers of either
SrTiO3 or of oxygen-rich BaFe2As2, can be used to control flux pinning, thereby
increasing critical fields and currents, without significantly affecting the
critical temperature of the pristine superconducting material. However, little
is known about the electron properties of these systems. Here we investigate
the electrodynamics of these superconducting pnictide superlattices in the
normal and superconducting state by using infrared reflectivity, from THz to
visible range. We find that multi-gap structure of these superlattices is
preserved, whereas some significant changes are observed in their electronic
structure with respect to those of the original pnictide. Our results suggest
that possible attempts to further increase the flux pinning may lead to a
breakdown of the pnictide superconducting properties.Comment: 4 pages, two figure
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