184 research outputs found
Giant Quantum Reflection of Neon Atoms from a Ridged Silicon Surface
The specular reflectivity of slow, metastable neon atoms from a silicon
surface was found to increase markedly when the flat surface was replaced by a
grating structure with parallel narrow ridges. For a surface with ridges that
have a sufficiently narrow top, the reflectivity was found to increase more
than two orders of magnitude at the incident angle of 10 mRad from the surface.
The slope of the reflectivity vs the incident angle near zero was found to be
nearly an order of magnitude smaller than that of a flat surface. A grating
with 6.5% efficiency for the first-order diffraction was fabricated by using
the ridged surface structure.Comment: 5 pages, 4 figures. To be published in J. Phys. Soc. Jp
The role of the glucose-sensing transcription factor carbohydrate-responsive element-binding protein pathway in termite queen fertility [plus Correction]
Modeling and Optimization of Lactic Acid Synthesis by the Alkaline Degradation of Fructose in a Batch Reactor
The present work deals with the determination of the optimal operating conditions of lactic acid synthesis by the alkaline degradation of fructose. It is a complex transformation for which detailed knowledge is not available. It is carried out in a batch
or semi-batch reactor. The ‘‘Tendency Modeling’’ approach, which consists of the development of an approximate stoichiometric and kinetic model, has been used.
An experimental planning method has been utilized as the database for model development.
The application of the experimental planning methodology allows comparison between the experimental and model response. The model is then used in an optimization procedure to compute the optimal process. The optimal control problem is converted into a nonlinear programming problem solved using the sequencial quadratic programming procedure coupled with the golden search method. The strategy developed allows simultaneously optimizing the different variables, which may be constrained. The validity of the methodology is illustrated by the determination
of the optimal operating conditions of lactic acid production
Resolved diffraction patterns from a reflection grating for atoms
We have studied atomic diffraction at normal incidence from an evanescent
standing wave with a high resolution using velocity selective Raman
transitions. We have observed up to 3 resolved orders of diffraction, which are
well accounted for by a scalar diffraction theory. In our experiment the
transverse coherence length of the source is greater than the period of the
diffraction grating.Comment: 8 pages, 4 figure
Properties of Microelectromagnet Mirrors as Reflectors of Cold Rb Atoms
Cryogenically cooled microelectromagnet mirrors were used to reflect a cloud
of free-falling laser-cooled 85Rb atoms at normal incidence. The mirrors
consisted of microfabricated current-carrying Au wires in a periodic serpentine
pattern on a sapphire substrate. The fluorescence from the atomic cloud was
imaged after it had bounced off a mirror. The transverse width of the cloud
reached a local minimum at an optimal current corresponding to minimum mirror
roughness. A distinct increase in roughness was found for mirror configurations
with even versus odd number of lines. These observations confirm theoretical
predictions.Comment: Physical Review A, in print; 11 pages, 4 figure
The MRN complex is transcriptionally regulated by MYCN during neural cell proliferation to control replication stress
The MRE11/RAD50/NBS1 (MRN) complex is a major sensor of DNA double strand breaks, whose role in controlling faithful DNA replication and preventing replication stress is also emerging. Inactivation of the MRN complex invariably leads to developmental and/or degenerative neuronal defects, the pathogenesis of which still remains poorly understood. In particular, NBS1 gene mutations are associated with microcephaly and strongly impaired cerebellar development, both in humans and in the mouse model. These phenotypes strikingly overlap those induced by inactivation of MYCN, an essential promoter of the expansion of neuronal stem and progenitor cells, suggesting that MYCN and the MRN complex might be connected on a unique pathway essential for the safe expansion of neuronal cells. Here, we show that MYCN transcriptionally controls the expression of each component of the MRN complex. By genetic and pharmacological inhibition of the MRN complex in a MYCN overexpression model and in the more physiological context of the Hedgehog-dependent expansion of primary cerebellar granule progenitor cells, we also show that the MRN complex is required for MYCN-dependent proliferation. Indeed, its inhibition resulted in DNA damage, activation of a DNA damage response, and cell death in a MYCN- and replication-dependent manner. Our data indicate the MRN complex is essential to restrain MYCN-induced replication stress during neural cell proliferation and support the hypothesis that replication-born DNA damage is responsible for the neuronal defects associated with MRN dysfunctions.Cell Death and Differentiation advance online publication, 12 June 2015; doi:10.1038/cdd.2015.81
PEG Branched Polymer for Functionalization of Nanomaterials with Ultralong Blood Circulation
Nanomaterials have been actively pursued for biological and medical
applications in recent years. Here, we report the synthesis of several new
poly(ethylene glycol) grafted branched-polymers for functionalization of
various nanomaterials including carbon nanotubes, gold nanoparticles (NP) and
gold nanorods (NRs), affording high aqueous solubility and stability for these
materials. We synthesize different surfactant polymers based upon
poly-(g-glutamic acid) (gPGA) and poly(maleic anhydride-alt-1-octadecene)
(PMHC18). We use the abundant free carboxylic acid groups of gPGA for attaching
lipophilic species such as pyrene or phospholipid, which bind to nanomaterials
via robust physisorption. Additionally, the remaining carboxylic acids on gPGA
or the amine-reactive anhydrides of PMHC18 are then PEGylated, providing
extended hydrophilic groups, affording polymeric amphiphiles. We show that
single-walled carbon nanotubes (SWNTs), Au NPs and NRs functionalized by the
polymers exhibit high stability in aqueous solutions at different pHs, at
elevated temperatures and in serum. Morever, the polymer-coated SWNTs exhibit
remarkably long blood circulation (t1/2 22.1 h) upon intravenous injection into
mice, far exceeding the previous record of 5.4 h. The ultra-long blood
circulation time suggests greatly delayed clearance of nanomaterials by the
reticuloendothelial system (RES) of mice, a highly desired property for in vivo
applications of nanomaterials, including imaging and drug delivery
Mechanics of the IL2RA Gene Activation Revealed by Modeling and Atomic Force Microscopy
Transcription implies recruitment of RNA polymerase II and transcription factors (TFs) by DNA melting near transcription start site (TSS). Combining atomic force microscopy and computer modeling, we investigate the structural and dynamical properties of the IL2RA promoter and identify an intrinsically negative supercoil in the PRRII region (containing Elf-1 and HMGA1 binding sites), located upstream of a curved DNA region encompassing TSS. Conformational changes, evidenced by time-lapse studies, result in the progressive positioning of curvature apex towards the TSS, likely facilitating local DNA melting. In vitro assays confirm specific binding of the General Transcription Factors (GTFs) TBP and TFIIB over TATA-TSS position, where an inhibitory nucleosome prevented preinitiation complex (PIC) formation and uncontrolled DNA melting. These findings represent a substantial advance showing, first, that the structural properties of the IL2RA promoter are encoded in the DNA sequence and second, that during the initiation process DNA conformation is dynamic and not static
Mono- and Biexponential Luminescence Decays of Individual Single-Walled Carbon Nanotubes
COUP-TFII Controls Mouse Pancreatic β-Cell Mass through GLP-1-β-Catenin Signaling Pathways
Background: The control of the functional pancreatic beta-cell mass serves the key homeostatic function of releasing the right amount of insulin to keep blood sugar in the normal range. It is not fully understood though how beta-cell mass is determined
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