302 research outputs found
Relativistic diffusion processes and random walk models
The nonrelativistic standard model for a continuous, one-parameter diffusion
process in position space is the Wiener process. As well-known, the Gaussian
transition probability density function (PDF) of this process is in conflict
with special relativity, as it permits particles to propagate faster than the
speed of light. A frequently considered alternative is provided by the
telegraph equation, whose solutions avoid superluminal propagation speeds but
suffer from singular (non-continuous) diffusion fronts on the light cone, which
are unlikely to exist for massive particles. It is therefore advisable to
explore other alternatives as well. In this paper, a generalized Wiener process
is proposed that is continuous, avoids superluminal propagation, and reduces to
the standard Wiener process in the non-relativistic limit. The corresponding
relativistic diffusion propagator is obtained directly from the nonrelativistic
Wiener propagator, by rewriting the latter in terms of an integral over
actions. The resulting relativistic process is non-Markovian, in accordance
with the known fact that nontrivial continuous, relativistic Markov processes
in position space cannot exist. Hence, the proposed process defines a
consistent relativistic diffusion model for massive particles and provides a
viable alternative to the solutions of the telegraph equation.Comment: v3: final, shortened version to appear in Phys. Rev.
Electrostatic considerations affecting the calculated HOMO-LUMO gap in protein molecules.
A detailed study of energy differences between the highest occupied and
lowest unoccupied molecular orbitals (HOMO-LUMO gaps) in protein systems and
water clusters is presented. Recent work questioning the applicability of
Kohn-Sham density-functional theory to proteins and large water clusters (E.
Rudberg, J. Phys.: Condens. Mat. 2012, 24, 072202) has demonstrated vanishing
HOMO-LUMO gaps for these systems, which is generally attributed to the
treatment of exchange in the functional used. The present work shows that the
vanishing gap is, in fact, an electrostatic artefact of the method used to
prepare the system. Practical solutions for ensuring the gap is maintained when
the system size is increased are demonstrated. This work has important
implications for the use of large-scale density-functional theory in
biomolecular systems, particularly in the simulation of photoemission, optical
absorption and electronic transport, all of which depend critically on
differences between energies of molecular orbitals.Comment: 13 pages, 4 figure
Diffusion in the special theory of relativity
The Markovian diffusion theory is generalized within the framework of the
special theory of relativity using a modification of the mathematical calculus
of diffusion on Riemannian manifolds (with definite metric) to describe
diffusion on Lorentzian manifolds with an indefinite metric. A generalized
Langevin equation in the fiber space of position, velocity and orthonormal
velocity frames is defined from which the generalized relativistic Kramers
equation in the phase space in external force fields is derived. The obtained
diffusion equation is invariant under Lorentz transformations and its
stationary solution is given by the J\"{u}ttner distribution. Besides a
non-stationary analytical solution is derived for the example of force-free
relativistic diffusion.Comment: 10 pages, 1 figur
Selective serotonin reuptake inhibitors (SSRIs) for stroke recovery
BACKGROUND: Selective serotonin reuptake inhibitors (SSRIs) might theoretically reduce post‐stroke disability by direct effects on the brain. This Cochrane Review was first published in 2012 and last updated in 2019. OBJECTIVES: To determine if SSRIs are more effective than placebo or usual care at improving outcomes in people less than 12 months post‐stroke, and to determine whether treatment with SSRIs is associated with adverse effects. SEARCH METHODS: We searched the Cochrane Stroke Group Trials Register (last searched 7 January 2021), Cochrane Controlled Trials Register (CENTRAL, Issue 7 of 12, 7 January 2021), MEDLINE (1946 to 7 January 2021), Embase (1974 to 7 January 2021), CINAHL (1982 to 7 January 2021), PsycINFO (1985 to 7 January 2021), and AMED (1985 to 7 January 2021). PsycBITE had previously been searched (16 July 2018). We searched clinical trials registers. SELECTION CRITERIA: We included randomised controlled trials (RCTs) recruiting stroke survivors within the first year. The intervention was any SSRI, at any dose, for any period, and for any indication. The comparator was usual care or placebo. Studies reporting at least one of our primary (disability score or independence) or secondary outcomes (impairments, depression, anxiety, quality of life, fatigue, cognition, healthcare cost, death, adverse events and leaving the study early) were included in the meta‐analysis. The primary analysis included studies at low risk of bias. DATA COLLECTION AND ANALYSIS: We extracted data on demographics, stroke type and, our pre‐specified outcomes, and bias sources. Two review authors independently extracted data. We used mean difference (MD) or standardised mean differences (SMDs) for continuous variables, and risk ratios (RRs) for dichotomous variables, with 95% confidence intervals (CIs). We assessed bias risks and applied GRADE criteria. MAIN RESULTS: We identified 76 eligible studies (13,029 participants); 75 provided data at end of treatment, and of these two provided data at follow‐up. Thirty‐eight required participants to have depression to enter. The duration, drug, and dose varied. Six studies were at low risk of bias across all domains; all six studies did not need participants to have depression to enter, and all used fluoxetine. Of these six studies, there was little to no difference in disability between groups SMD ‐0.0; 95% CI ‐0.05 to 0.05; 5 studies, 5436 participants, high‐quality evidence) or in independence (RR 0.98; 95% CI 0.93 to 1.03; 5 studies, 5926 participants; high‐quality evidence) at the end of treatment. In the studies at low risk of bias across all domains, SSRIs slightly reduced the average depression score (SMD 0.14 lower, 95% CI 0.19 lower to 0.08 lower; 4 studies; 5356 participants, high‐quality evidence) and there was a slight reduction in the proportion with depression (RR 0.75, 95% CI 0.65 to 0.86; 3 studies, 5907 participants, high‐quality evidence). Cognition was slightly better in the control group (MD ‐1.22, 95% CI ‐2.37 to ‐0.07; 4 studies, 5373 participants, moderate‐quality evidence). Only one study (n = 30) reported neurological deficit score (SMD ‐0.39, 95% CI ‐1.12 to 0.33; low‐quality evidence). SSRIs resulted in little to no difference in motor deficit (SMD 0.03, ‐0.02 to 0.08; 6 studies, 5518 participants, moderate‐quality evidence). SSRIs slightly increased the proportion leaving the study early (RR 1.57, 95% CI 1.03 to 2.40; 6 studies, 6090 participants, high‐quality evidence). SSRIs slightly increased the outcome of a seizure (RR 1.40, 95% CI 1.00 to 1.98; 6 studies, 6080 participants, moderate‐quality evidence) and a bone fracture (RR 2.35, 95% CI 1.62 to 3.41; 6 studies, 6080 participants, high‐quality evidence). One study at low risk of bias across all domains reported gastrointestinal side effects (RR 1.71, 95% CI 0.33, to 8.83; 1 study, 30 participants). There was no difference in the total number of deaths between SSRI and placebo (RR 1.01, 95% CI 0.82 to 1.24; 6 studies, 6090 participants, moderate quality evidence). SSRIs probably result in little to no difference in fatigue (MD ‐0.06; 95% CI ‐1.24 to 1.11; 4 studies, 5524 participants, moderate‐quality of evidence), nor in quality of life (MD 0.00; 95% CI ‐0.02 to 0.02, 3 studies, 5482 participants, high‐quality evidence). When all studies, irrespective of risk of bias, were included, SSRIs reduced disability scores but not the proportion independent. There was insufficient data to perform a meta‐analysis of outcomes at end of follow‐up. Several small ongoing studies are unlikely to alter conclusions. AUTHORS' CONCLUSIONS: There is high‐quality evidence that SSRIs do not make a difference to disability or independence after stroke compared to placebo or usual care, reduced the risk of future depression, increased bone fractures and probably increased seizure risk
Idiopathic osteonecrosis of the medial tibial plateau
Osteonecrosis of the medial tibial plateau is characterized by acute pain on the medial aspect of the knee. Progression can lead to articular collapse and requires early diagnosis and treatment. We studied seven patients affected of idiopathic osteonecrosis of the tibial plateau. The mean age was 62 years and the mean follow-up 42 months. We performed roentgenograms in all patients, bone scans in three patients and magnetic resonance image (MRI) in five. MRI shows T1-weighted low-intensity signal and T2-weighted high-intensity signal with a surrounding area of intermediate low-intensity signal. An increased focal uptake was seen at bone scan. Histological findings showed necrotic bone with empty lacunae. Surgical treatment consisted of tibial subchondral drilling in four patients-two of them by failure of conservative treatment, and a total knee arthroplasty in other two. One patient had a satisfactory evolution with conservative treatment. Idiopathic osteonecrosis of the tibial plateau must be considered in elderly patients with knee pain over the medial tibial plateau. At early stages, decompression with tibial drilling must be considered. This procedure allows a prompt and effective relief of symptom
Maternal but Not Paternal Association of Ambulatory Blood Pressure With Albumin Excretion in Young Offspring With Type 1 Diabetes
OBJECTIVE: Familial predisposition to hypertension has been associated with the development of diabetic nephropathy in adults, but there are limited data in adolescents. Our aim was to assess whether parental ambulatory blood pressure (ABP) was associated with ABP and albumin excretion in young offspring with type 1 diabetes. RESEARCH DESIGN AND METHODS: Twenty-four-hour ABP monitoring was performed in 509 young offspring (mean +/- SD age 15.8 +/- 2.3 years) with type 1 diabetes, 311 fathers, and 444 mothers. Systolic (SBP) and diastolic blood pressure (DBP) measurements during 24 h, daytime, and nighttime were calculated. Three early morning urinary albumin-to-creatinine ratios (ACRs), A1C, and anthropometric parameters were available for the offspring. RESULTS: All paternal ABP parameters, except for nighttime SBP, were independently related to the offspring's ABP (24-h SBP beta = 0.18, 24-h DBP beta = 0.22, daytime SBP beta = 0.25, daytime DBP beta = 0.23, and nighttime DBP beta = 0.18; all P < 0.01). Maternal 24-h DBP (beta = 0.19, P = 0.004), daytime DBP (beta = 0.09, P = 0.04), and nighttime SBP (beta = 0.24 P = 0.001) were related to the corresponding ABP parameter in the offspring. Significant associations were found between the offspring's logACR and maternal ABP. The association with 24-h DBP (beta = 0.16, P = 0.02), daytime DBP (beta = 0.16 P = 0.02), and nighttime DBP (beta = 0.15 P = 0.03) persisted even after adjustment for the offspring's ABP. Mothers of offspring with microalbuminuria had higher ABP than mothers of offspring without microalbuminuria (all P < 0.05). CONCLUSIONS: In this cohort, parental ABP significantly influenced offspring blood pressure, therefore confirming familial influences on this trait. In addition, maternal ABP, particularly DBP, was closely related to ACR in the offspring, suggesting a dominant effect of maternal genes or an effect of the intrauterine environment on microalbuminuria risk
O(N) methods in electronic structure calculations
Linear scaling methods, or O(N) methods, have computational and memory
requirements which scale linearly with the number of atoms in the system, N, in
contrast to standard approaches which scale with the cube of the number of
atoms. These methods, which rely on the short-ranged nature of electronic
structure, will allow accurate, ab initio simulations of systems of
unprecedented size. The theory behind the locality of electronic structure is
described and related to physical properties of systems to be modelled, along
with a survey of recent developments in real-space methods which are important
for efficient use of high performance computers. The linear scaling methods
proposed to date can be divided into seven different areas, and the
applicability, efficiency and advantages of the methods proposed in these areas
is then discussed. The applications of linear scaling methods, as well as the
implementations available as computer programs, are considered. Finally, the
prospects for and the challenges facing linear scaling methods are discussed.Comment: 85 pages, 15 figures, 488 references. Resubmitted to Rep. Prog. Phys
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Purification and functional characterisation of rhiminopeptidase A, a novel aminopeptidase from the venom of Bitis gabonica rhinoceros
This study describes the discovery and characterisation of a novel aminopeptidase A from the venom of B. g. rhinoceros and highlights its potential biological importance. Similar to mammalian aminopeptidases, rhiminopeptidase A might be capable of playing roles in altering the blood pressure and brain function of victims. Furthermore, it could have additional effects on the biological functions of other host proteins by cleaving their N-terminal amino acids. This study points towards the importance of complete analysis of individual components of snake venom in order to develop effective therapies for snake bites
Towards Graphene Nanoribbon-based Electronics
The successful fabrication of single layer graphene has greatly stimulated
the progress of the research on graphene. In this article, focusing on the
basic electronic and transport properties of graphene nanoribbons (GNRs), we
review the recent progress of experimental fabrication of GNRs, and the
theoretical and experimental investigations of physical properties and device
applications of GNRs. We also briefly discuss the research efforts on the spin
polarization of GNRs in relation to the edge states.Comment: 9pages,10figure
Molecular Dynamics Simulation Study and Hybrid Pharmacophore Model Development in Human LTA4H Inhibitor Design
Human leukotriene A4 hydrolase (hLTA4H) is a bi-functional enzyme catalyzes the hydrolase and aminopeptidase functions upon the fatty acid and peptide substrates, respectively, utilizing the same but overlapping binding site. Particularly the hydrolase function of this enzyme catalyzes the rate-limiting step of the leukotriene (LT) cascade that converts the LTA4 to LTB4. This product is a potent pro-inflammatory activator of inflammatory responses and thus blocking this conversion provides a valuable means to design anti-inflammatory agents. Four structurally very similar chemical compounds with highly different inhibitory profile towards the hydrolase function of hLTA4H were selected from the literature. Molecular dynamics (MD) simulations of the complexes of hLTA4H with these inhibitors were performed and the results have provided valuable information explaining the reasons for the differences in their biological activities. Binding mode analysis revealed that the additional thiophene moiety of most active inhibitor helps the pyrrolidine moiety to interact the most important R563 and K565 residues. The hLTA4H complexes with the most active compound and substrate were utilized in the development of hybrid pharmacophore models. These developed pharmacophore models were used in screening chemical databases in order to identify lead candidates to design potent hLTA4H inhibitors. Final evaluation based on molecular docking and electronic parameters has identified three compounds of diverse chemical scaffolds as potential leads to be used in novel and potent hLTA4H inhibitor design
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