1,384 research outputs found
Remote functionalisation via sodium alkylamidozincate intermediates : access to unusual fluorenone and pyridyl ketone reactivity patterns
Treating fluorenone or 2-benzoylpyridine with the sodium zincate [(TMEDA)center dot Na(mu-Bu-t)(mu-TMP)Zn(Bu-t)] in hexane solution, gives efficient Bu-t addition across the respective organic substrate in a highly unusual 1,6-fashion, producing isolable organometallic intermediates which can be quenched and aerobically oxidised to give 3-tert-butyl-9H-fluoren-9-one and 2-benzoyl-5-tert-butylpyridine respectively
Semiclassical model of ultrafast photoisomerization reactions
In this letter we propose a model which explains ultrafast and efficient
photoisomerization reactions as driven by transitions between quasistationary
states of one dimensional (1D) double well potential of an excited electronic
state. This adiabatic potential is formed as a result of doubly crossing of a
decay diabatic potential of the ground electronic state and a bound diabatic
potential of the excited state. We calculate the eigenstates and eigenfunctions
using the semiclassical connection matrices at the turning and crossing points
and the shift matrices between these points. The transitions between the
localized in the wells below the adiabatic barrier states are realized by the
tunneling and by the double non-adiabatic transitions via the crossing points
processes. Surprisingly the behavior with the maximum transition rate keeps
going even for the states relatively far above the barrier (2 -4 times the
barrier height). Even though a specific toy model is investigated here, when
properly interpreted it yields quite reasonable values for a variety of
measured quantities, such as a reaction quantum yield, and conversion time.Comment: 9 pages, 5 figures. accepted to Chem. Phys. Letters (2005
The analysis on the single particle model of CDW
Gruner put forward a single particle model of charge-density wave, which is a
typical nonlinear differential equation, and also a mathematical model of
pendulum. This Letter analyzes the solution of equation by the rotated vector
fields theory, providing the relation between the applied field E and the
periodic solution, and the conclusion that the critical value of E for the
periodic solution is fixed in the over-damped situation. With these
conclusions, it derives the formulae of nonlinear conductivity, narrow-band
noise, which are consistent with the empirical ones given by Fleming.Comment: This is a version with a physics focus, the part with a mathematical
focus is submitted at arXiv:0807.328
A reduced complexity numerical method for optimal gate synthesis
Although quantum computers have the potential to efficiently solve certain
problems considered difficult by known classical approaches, the design of a
quantum circuit remains computationally difficult. It is known that the optimal
gate design problem is equivalent to the solution of an associated optimal
control problem, the solution to which is also computationally intensive.
Hence, in this article, we introduce the application of a class of numerical
methods (termed the max-plus curse of dimensionality free techniques) that
determine the optimal control thereby synthesizing the desired unitary gate.
The application of this technique to quantum systems has a growth in complexity
that depends on the cardinality of the control set approximation rather than
the much larger growth with respect to spatial dimensions in approaches based
on gridding of the space, used in previous literature. This technique is
demonstrated by obtaining an approximate solution for the gate synthesis on
- a problem that is computationally intractable by grid based
approaches.Comment: 8 pages, 4 figure
Waveguiding and nonlinear optical properties of three-dimensional waveguides in LiTaO<inf>3</inf> written by high-repetition rate ultrafast laser
We report the fabrication of waveguides in lithium tantalate using a 250 kHz high-repetition rate ultrafast laser at 771 nm and the characterization of the resulting laser induced structure with second harmonic microscopy. Waveguides operating at the 1.5 μm telecommunication wavelength were formed above and below the focal volume using pulse energies ranging from 100 to 1.6 J and translation speeds from 100 μms to 5 mms. The second harmonic microscopy reveals no degradation of the electro-optic coefficient in the guiding region above the focal volume. © 2008 American Institute of Physics
Glaciers in the Canadian Columbia Basin, Technical Report
The cryosphere - all forms of frozen water on Earth- plays a fundamental role in its climate system. Seasonal snow, mountain glaciers, ice sheets, and sea ice reflect much of the incoming shortwave radiation at high latitudes and in mountainous terrain back to space, helping to regulate the surface temperature of the planet. Accelerating concentrations of greenhouse gases (Solomon et al. 2009) are responsible for late twentieth and early twenty-first century tropospheric warming; this warming in turn drives large-scale changes in the cryosphere, with global implications that include changes in hemispheric circulation (Francis and Vavrus 2012), sea level rise (Gardner et al. 2013) and increased warming through ice-albedo feedbacks
Templated deprotonative metalation of polyaryl systems : facile access to simple, previously inaccessible multi-iodoarenes
The development of new methodologies to affect non-ortho functionalization of arenes has emerged as a globally important arena for research, which is key to both fundamental studies and applied technologies. Here, a range of simple arene feedstocks (namely, biphenyl, meta-terphenyl, para-terphenyl, 1,3,5-triphenylbenzene and biphenylene) are transformed to hitherto unobtainable multi-iodoarenes via a s-block metal sodium magnesiate templated deprotonative approach. These iodoarenes have potential to be used in a whole host of high impact transformations, as precursors to key materials in the pharmaceutical, molecular electronic and nanomaterials industries. Proving the concept, we have transformed biphenyl to 3,5-bis(N-carbazolyl)-1,1’-biphenyl, a novel isomer of 4,4’-bis(N-carbazolyl)-1,1’-biphenyl (CPB) which is currently widely employed as a host material for organic light-emitting diodes, OLEDs
Assessing cognitive dysfunction in Parkinson's disease: An online tool to detect visuo-perceptual deficits.
BackgroundPeople with Parkinson's disease (PD) who develop visuo-perceptual deficits are at higher risk of dementia, but we lack tests that detect subtle visuo-perceptual deficits and can be performed by untrained personnel. Hallucinations are associated with cognitive impairment and typically involve perception of complex objects. Changes in object perception may therefore be a sensitive marker of visuo-perceptual deficits in PD.ObjectiveWe developed an online platform to test visuo-perceptual function. We hypothesised that (1) visuo-perceptual deficits in PD could be detected using online tests, (2) object perception would be preferentially affected, and (3) these deficits would be caused by changes in perception rather than response bias.MethodsWe assessed 91 people with PD and 275 controls. Performance was compared using classical frequentist statistics. We then fitted a hierarchical Bayesian signal detection theory model to a subset of tasks.ResultsPeople with PD were worse than controls at object recognition, showing no deficits in other visuo-perceptual tests. Specifically, they were worse at identifying skewed images (P < .0001); at detecting hidden objects (P = .0039); at identifying objects in peripheral vision (P < .0001); and at detecting biological motion (P = .0065). In contrast, people with PD were not worse at mental rotation or subjective size perception. Using signal detection modelling, we found this effect was driven by change in perceptual sensitivity rather than response bias.ConclusionsOnline tests can detect visuo-perceptual deficits in people with PD, with object recognition particularly affected. Ultimately, visuo-perceptual tests may be developed to identify at-risk patients for clinical trials to slow PD dementia. © 2018 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society
Promoting remyelination through cell transplantation therapies in a model of viral-induced neurodegenerative disease.
Multiple sclerosis (MS) is a central nervous system (CNS) disease characterized by chronic neuroinflammation, demyelination, and axonal damage. Infiltration of activated lymphocytes and myeloid cells are thought to be primarily responsible for white matter damage and axonopathy. Several United States Food and Drug Administration-approved therapies exist that impede activated lymphocytes from entering the CNS thereby limiting new lesion formation in patients with relapse-remitting forms of MS. However, a significant challenge within the field of MS research is to develop effective and sustained therapies that allow for axonal protection and remyelination. In recent years, there has been increasing evidence that some kinds of stem cells and their derivatives seem to be able to mute neuroinflammation as well as promote remyelination and axonal integrity. Intracranial infection of mice with the neurotropic JHM strain of mouse hepatitis virus (JHMV) results in immune-mediated demyelination and axonopathy, making this an excellent model to interrogate the therapeutic potential of stem cell derivatives in evoking remyelination. This review provides a succinct overview of our recent findings using intraspinal injection of mouse CNS neural progenitor cells and human neural precursors into JHMV-infected mice. JHMV-infected mice receiving these cells display extensive remyelination associated with axonal sparing. In addition, we discuss possible mechanisms associated with sustained clinical recovery. Developmental Dynamics 248:43-52, 2019. © 2018 Wiley Periodicals, Inc
Modeling postbreakup landscape development and denudational history across the southeast African (Drakensberg Escarpment) margin
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