11,472 research outputs found
Study on the conformation of insulin by solvent perturbation and ultraviolet spectroscopy
This study attempted to gain an insight of the conformation of insulin using solvent perturbation and ultraviolet spectroscopy. The effects of two solvents, mercaptoethanol and sucrose on the absorption spectrum of Insulin were studied; changes in ionic strength and pH were used to identify the position of amino acid chromophores. The effect on the absorption spectrum of movement from a non-polar to a polar environment indicates that tyrosine and phenylalanine reside on the surface of insulin protein. The results show that pH resolved spectral behavior of Insulin in the neighborhood of 290 nm is determined predominantly by the ionization of imidazole â NH+ of histidine. The results, however, do not rule out the possible contribution of the phenol hydroxyl of tyrosine in the spectral behavior. © 2013 International Formulae Group. All rights reserved.Keywords: Insulin conformation, solvent perturbation, ultraviolet spectroscopy
Splicing-dependent NMD does not require the EJC in Schizosaccharomyces pombe
Nonsense-mediated mRNA decay (NMD) is a translation-linked process that destroys mRNAs with premature translation termination codons (PTCs). In mammalian cells, NMD is also linked to pre-mRNA splicing, usually PTCs trigger strong NMD only when positioned upstream of at least one intron. The exon junction complex (EJC) is believed to mediate the link between splicing and NMD in these systems. Here, we report that in Schizosaccharomyces pombe splicing also enhances NMD, but against the EJC model prediction, an intron stimulated NMD regardless of whether it is positioned upstream or downstream of the PTC and EJC components are not required. Still the effect of splicing seems to be directâwe have found that the important NMD determinant is the proximity of an intron to the PTC, not just the occurrence of splicing. On the basis of these results, we propose a new model to explain how splicing could affect NMD
Recommended from our members
Why are nitrogenâfixing trees rare at higher compared to lower latitudes?
Symbiotic nitrogen (N) fixation provides a dominant source of new N to the terrestrial biosphere, yet in many cases the abundance of Nâfixing trees appears paradoxical. Nâfixing trees, which should be favored when N is limiting, are rare in higher latitude forests where N limitation is common, but are abundant in many lower latitude forests where N limitation is rare. Here, we develop a graphical and mathematical model to resolve the paradox. We use the model to demonstrate that N fixation is not necessarily cost effective under all degrees of N limitation, as intuition suggests. Rather, N fixation is only cost effective when N limitation is sufficiently severe. This general finding, specific versions of which have also emerged from other models, would explain sustained moderate N limitation because Nâfixing trees would either turn N fixation off or be outcompeted under moderate N limitation. From this finding, four general hypothesis classes emerge to resolve the apparent paradox of N limitation and Nâfixing tree abundance across latitude. The first hypothesis is that N limitation is less common at higher latitudes. This hypothesis contradicts prevailing evidence, so is unlikely, but the following three hypotheses all seem likely. The second hypothesis, which is new, is that even if N limitation is more common at higher latitudes, more severe N limitation might be more common at lower latitudes because of the capacity for higher N demand. Third, N fixation might be cost effective under milder N limitation at lower latitudes but only under more severe N limitation at higher latitudes. This third hypothesis class generalizes previous hypotheses and suggests new specific hypotheses. For example, greater tradeâoffs between N fixation and N use efficiency, soil N uptake, or plant turnover at higher compared to lower latitudes would make N fixation cost effective only under more severe N limitation at higher latitudes. Fourth, Nâfixing trees might adjust N fixation more at lower than at higher latitudes. This framework provides new hypotheses to explain the latitudinal abundance distribution of Nâfixing trees, and also provides a new way to visualize them. Therefore, it can help explain the seemingly paradoxical persistence of N limitation in many higher latitude forests
Brick Walls and AdS/CFT
We discuss the relationship between the bulk-boundary correspondence in
Rehren's algebraic holography (and in other 'fixed-background' approaches to
holography) and in mainstream 'Maldacena AdS/CFT'. Especially, we contrast the
understanding of black-hole entropy from the viewpoint of QFT in curved
spacetime -- in the framework of 't Hooft's 'brick wall' model -- with the
understanding based on Maldacena AdS/CFT. We show that the brick-wall
modification of a Klein Gordon field in the Hartle-Hawking-Israel state on
1+2-Schwarzschild AdS (BTZ) has a well-defined boundary limit with the same
temperature and entropy as the brick-wall-modified bulk theory. One of our main
purposes is to point out a close connection, for general AdS/CFT situations,
between the puzzle raised by Arnsdorf and Smolin regarding the relationship
between Rehren's algebraic holography and mainstream AdS/CFT and the puzzle
embodied in the 'correspondence principle' proposed by Mukohyama and Israel in
their work on the brick-wall approach to black hole entropy. Working on the
assumption that similar results will hold for bulk QFT other than the Klein
Gordon field and for Schwarzschild AdS in other dimensions, and recalling the
first author's proposed resolution to the Mukohyama-Israel puzzle based on his
'matter-gravity entanglement hypothesis', we argue that, in Maldacena AdS/CFT,
the algebra of the boundary CFT is isomorphic only to a proper subalgebra of
the bulk algebra, albeit (at non-zero temperature) the (GNS) Hilbert spaces of
bulk and boundary theories are still the 'same' -- the total bulk state being
pure, while the boundary state is mixed (thermal). We also argue from the
finiteness of its boundary (and hence, on our assumptions, also bulk) entropy
at finite temperature, that the Rehren dual of the Maldacena boundary CFT
cannot itself be a QFT and must, instead, presumably be something like a string
theory.Comment: 54 pages, 3 figures. Arguments strengthened in the light of B.S. Kay
`Instability of Enclosed Horizons' arXiv:1310.739
Oral health in Libya: addressing the future challenges
Libya is a vast country situated in North Africa, having a relatively better functioning economy with a scanty population. This article is the first known attempt to review the current state of oral health care in Libya and to explore the present trends and future challenges. Libyan health system, oral health care, and human resources with the present status of dental education are reviewed comprehensively. A bibliographic study of oral health research and publications has been carried out. The results point toward a common indicator that oral healthrelated research is low. Strategies have to be developed to educate the medical and dental professionals, to update the current curriculum and enable the system to be competent in all aspects of oral health care management.Keywords: oral health; oral health research; oral health care; dental research; dental education; Liby
Chromium isotopes in marine hydrothermal sediments
Hydrothermal chromium (Cr) cycling contributes to marine Cr inventories and their Cr isotopic composition, yet Cr isotope effects associated with this cycling remain poorly documented. Here we determine the distribution, isotopic composition, and diagenetic mobility of Cr in hydrothermal sediments from the distal flank of the South East Pacific Rise (SEPR, DSDP-site 598). We find that Cr is primarily associated with the metalliferous iron (oxyhydr) oxide and detrital components of the sediment (0.4â3.6âŻmgâŻkgâ»Âč), whereas Cr concentrations are much lower in the dominant carbonate phase (80% Cr from the sediment relative to Fe. We propose this loss is tied to oxidation of authigenic Cr(III) to Cr(VI) followed by diagenetic remobilization and efflux from the sediment pile. The bulk ÎŽâ”ÂłCr composition of the SEPR sediments is isotopically light (â0.24 to â0.57âŻÂ±âŻ0.05â°) and the authigenic ÎŽâ”ÂłCr is as light as â1.2âŻÂ±âŻ0.2â°, and we argue that this light Cr isotopic composition results from the partial reduction of oxic seawater-bearing Cr(VI) by reduced hydrothermal vent fluids enriched in Fe(II)aq. Diagenetic oxidation of the reactive Cr pool by Mn-oxides and loss of Cr(VI) from the sediment may further deplete the sediment in â”ÂłCr during diagenesis. The ÎŽâ”ÂłCr composition of the detrital Cr fraction of the sediment (average ÎŽâ”ÂłCr compositionâŻ=âŻâ0.05âŻÂ±âŻ0.04â°) falls within the igneous silicate earth (ISE) range, revealing that detrital Cr delivered to this region of the Pacific ocean is unfractionated, and has carried a relatively constant ÎŽâ”ÂłCr composition over the last 5.7âŻmillionâŻyears. Together our results show that light ÎŽâ”ÂłCr compositions in hydrothermal sediments are imparted through a combination of processes previously overlooked in the marine Cr biogeochemical cycle, and that the ÎŽâ”ÂłCr composition of such sediments may provide a rich source of information on paleo-marine redox conditions
An inflatable and wearable wireless system for making 32-channel electroencephalogram measurements
© 2001-2011 IEEE. Potable electroencephalography (EEG) devices have become critical for important research. They have various applications, such as in brain-computer interfaces (BCI). Numerous recent investigations have focused on the development of dry sensors, but few concern the simultaneous attachment of high-density dry sensors to different regions of the scalp to receive qualified EEG signals from hairy sites. An inflatable and wearable wireless 32-channel EEG device was designed, prototyped, and experimentally validated for making EEG signal measurements; it incorporates spring-loaded dry sensors and a novel gasbag design to solve the problem of interference by hair. The cap is ventilated and incorporates a circuit board and battery with a high-tolerance wireless (Bluetooth) protocol and low power consumption characteristics. The proposed system provides a 500/250 Hz sampling rate, and 24 bit EEG data to meet the BCI system data requirement. Experimental results prove that the proposed EEG system is effective in measuring audio event-related potential, measuring visual event-related potential, and rapid serial visual presentation. Results of this work demonstrate that the proposed EEG cap system performs well in making EEG measurements and is feasible for practical applications
A novel 16-channel wireless system for electroencephalography measurements with dry spring-loaded sensors
Understanding brain function using electroencephalography (EEG) is an important issue for cerebral nervous system diseases, especially for epilepsy and Alzheimer's disease. Many EEG measurement systems are used reliably to study these diseases, but their bulky size and the use of wet sensors make them uncomfortable and inconvenient for users. To overcome the limitations of conventional EEG measurement systems, a wireless and wearable multichannel EEG measurement system is proposed in this paper. This system includes a wireless data acquisition device, dry spring-loaded sensors, and a sizeadjustable soft cap. We compared the performance of the proposed system using dry versus conventional wet sensors. A significant positive correlation between readings from wet and dry sensors was achieved, thus demonstrating the performance of the system. Moreover, four different features of EEG signals (i.e., normal, eye-blinking, closed-eyes, and teeth-clenching signals) were measured by 16 dry sensors to ensure that they could be detected in real-life cognitive neuroscience applications. Thus, we have shown that it is possible to reliably measure EEG signals using the proposed system. This paper presents novel insights into the field of cognitive neuroscience, showing the possibility of studying brain function under real-life conditions. © 2014 IEEE
Deformation of Codimension-2 Surface and Horizon Thermodynamics
The deformation equation of a spacelike submanifold with an arbitrary
codimension is given by a general construction without using local frames. In
the case of codimension-1, this equation reduces to the evolution equation of
the extrinsic curvature of a spacelike hypersurface. In the more interesting
case of codimension-2, after selecting a local null frame, this deformation
equation reduces to the well known (cross) focusing equations. We show how the
thermodynamics of trapping horizons is related to these deformation equations
in two different formalisms: with and without introducing quasilocal energy. In
the formalism with the quasilocal energy, the Hawking mass in four dimension is
generalized to higher dimension, and it is found that the deformation of this
energy inside a marginal surface can be also decomposed into the contributions
from matter fields and gravitational radiation as in the four dimension. In the
formalism without the quasilocal energy, we generalize the definition of slowly
evolving future outer trapping horizons proposed by Booth to past trapping
horizons. The dynamics of the trapping horizons in FLRW universe is given as an
example. Especially, the slowly evolving past trapping horizon in the FLRW
universe has close relation to the scenario of slow-roll inflation. Up to the
second order of the slowly evolving parameter in this generalization, the
temperature (surface gravity) associated with the slowly evolving trapping
horizon in the FLRW universe is essentially the same as the one defined by
using the quasilocal energy.Comment: Latex, 61 pages, no figures; v2, type errors corrected; v3,
references and comments are added, English is improved, to appear in JHE
- âŠ