1,100 research outputs found
Quantum effects in the diffusion of hydrogen on Ru(0001)
An understanding of hydrogen diffusion on metal surfaces is important, not
just for its role in heterogeneous catalysis and hydrogen fuel cell technology,
but also because it provides model systems where tunneling can be studied under
well-defined conditions. Here we report helium spin-echo measurements of the
atomic-scale motion of hydrogen on the Ru(0001) surface between 75 and 250 K.
Quantum effects are evident at temperatures as high as 200 K, while below 120 K
we observe a tunneling-dominated temperature independent jump rate of
1.910 s, many orders of magnitude faster than previously
seen. Quantum transition state theory calculations based on ab initio
path-integral simulations reproduce the temperature dependence of the rate at
higher temperatures and predict a crossover to tunneling-dominated diffusion at
low temperatures, although the tunneling rate is under-estimated, highlighting
the need for future experimental and theoretical studies of hydrogen diffusion
on well-defined surfaces.Comment: 15 pages, 3 figure
Inherited retinal diseases: Therapeutics, clinical trials and end pointsβA review
Inherited retinal diseases (IRDs) are a clinically and genetically heterogeneous group of disorders characterised by photoreceptor degeneration or dysfunction. These disorders typically present with severe vision loss that can be progressive, with disease onset ranging from congenital to late adulthood. The advances in genetics, retinal imaging and molecular biology, have conspired to create the ideal environment for establishing treatments for IRDs, with the first approved gene therapy and the commencement of multiple clinical trials. The scope of this review is to familiarise clinicians and scientists with the current management and the prospects for novel therapies for: (1) macular dystrophies, (2) cone and coneβrod dystrophies, (3) cone dysfunction syndromes, (4) Leber congenital amaurosis, (5) rodβcone dystrophies, (6) rod dysfunction syndromes and (7) chorioretinal dystrophies. We also briefly summarise the investigated end points for the ongoing trials
Association of geopotential height patterns with heavy rainfall events in Cyprus
Dynamically induced rainfall is strongly connected with
synoptic atmospheric circulation patterns at the upper levels. This study
investigates the relationship between days of high precipitation volume
events in the eastern Mediterranean and the associated geopotential height
patterns at 500 hPa. To reduce the number of different patterns and to
simplify the statistical processing, the input days were classified into
clusters of synoptic cases having similar characteristics, by utilizing
Kohonen Self Organizing Maps (SOM) architecture. Using this architecture,
synoptic patterns were grouped into 9, 18, 27 and 36 clusters which were
subsequently used in the analysis. The classification performance was tested
by applying the method to extreme rainfall events in the eastern
Mediterranean. The relationship of the synoptic upper air patterns (500 hPa
height) and surface features (heavy rainfall events) was established, while
the 36 member classification proved to be the most efficient
The cold frontal depression that affected the area of Cyprus between 28 and 29 January 2008
The baroclinic depression that affected the area of Cyprus during the cold period, between 28 and 29 January 2008 was thoroughly studied and is presented in the present paper. A small perturbation on a northwesterly flow to the north of Cyprus has initiated the generation of the depression and in 24 h this developed into a deep baroclinic system. This depression was associated with intense weather phenomena, such as heavy thunderstorms with hail and near gale force winds. Strong cold advection resulted in a significant temperature decrease; precipitation even in lower altitudes was in the form of snow, while the accumulated rainfall corresponded to the 25% of the monthly normal. January 2008 is considered as a dry month, despite the fact that, on the average, January is considered as the wettest month of the year. In this study, the evolution and development of the depression was investigated from synoptic, dynamic, energetic and thermodynamic perspectives, in order to enhance our knowledge on the life cycle and behaviour of similar depressions over the area with extreme characteristics
OCT angiography in the management of choroidal neovascular membrane secondary to Sorsby fundus dystrophy
We describe the management of a woman aged 52 years with molecularly confirmed Sorsby fundus dystrophy, who presented with acute visual deterioration in her right eye. Fundus examination identified a right macular lesion suggestive of a choroidal neovascular membrane (CNVM). Optical coherence tomography angiography (OCTA) confirmed the presence of a CNVM. She was treated with 2 monthly intravitreal injections of bevacizumab, associated with OCTA evidence of regression of the CNVM and improvement in her visual acuity. OCTA is a novel, non-invasive method of imaging the retinal vasculature. Images are acquired rapidly, with no associated side effects, offering advantages over the current gold standard technique-fundus fluorescein angiography
Stargardt disease: clinical features, molecular genetics, animal models and therapeutic options
Stargardt disease (STGD1; MIM 248200) is the most prevalent inherited macular dystrophy and is associated with disease-causing sequence variants in the gene ABCA4 Significant advances have been made over the last 10β
years in our understanding of both the clinical and molecular features of STGD1, and also the underlying pathophysiology, which has culminated in ongoing and planned human clinical trials of novel therapies. The aims of this review are to describe the detailed phenotypic and genotypic characteristics of the disease, conventional and novel imaging findings, current knowledge of animal models and pathogenesis, and the multiple avenues of intervention being explored
Local investigation of femtosecond laser induced dynamics of water nanoclusters on Cu(111)
We explore the dynamics of low temperature interfacial water nanoclusters on Cu(111) by femtosecond-laser excitation, scanning tunneling microscopy and density functional theory. Laser illumination can be used to induce single molecules to diffuse within water clusters and across the surface, breaking and reforming hydrogen bonds. A linear diffusion probability with laser fluence is observed up to 0.6 J/m2 and we suggest that diffusion is initiated by hot electron attachment and detachment processes. The density functional calculations shed light on the detailed molecular mechanism for water diffusion that is determined by the local structure of the water clusters
A statistical analysis of sounding derived indices and parameters for extreme and non-extreme thunderstorm events over Cyprus
The main purpose of this study is to provide a simple
statistical analysis of several stability indices and
parameters for extreme and non-extreme thunderstorm events
during the period 1997 to 2001 in Cyprus. For this study,
radiosonde data from Athalassa station (35Β°1Β΄ N,
33Β°4Β΄ E) were analyzed during the aforementioned
period. The stability indices and parameters set under study
are the K index, the Total Totals (TT) index, the Convective
Available Potential Energy related parameters such as
Convective Available Potential Energy (CAPE),
Downdraft CAPE (DCAPE) and the Convective Inhibition (CIN), the Vorticity
Generator Parameter (VGP), the Bulk Richardson Number (BRN),
the BRN Shear and the Storm Relative Helicity (SRH). An
event is categorized as extreme, if primarily, CAPE was non
zero and secondary, if values of both the K and the
TotalTotals (TT) indices exceeded 26.9 and 50, respectively.
The cases with positive CAPE but lower values of the other
indices, were identified as non-extreme. By calculating the
median, the lower and upper limits, as well as the lower and
upper quartiles of the values of these indices, the main
characteristics of their distribution were determined
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