291 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
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
Using atomic interference to probe atom-surface interaction
We show that atomic interference in the reflection from two suitably
polarized evanescent waves is sensitive to retardation effects in the
atom-surface interaction for specific experimental parameters. We study the
limit of short and long atomic de Broglie wavelength. The former case is
analyzed in the semiclassical approximation (Landau-Zener model). The latter
represents a quantum regime and is analyzed by solving numerically the
associated coupled Schroedinger equations. We consider a specific experimental
scheme and show the results for rubidium (short wavelength) and the much
lighter meta-stable helium atom (long wavelength). The merits of each case are
then discussed.Comment: 11 pages, including 6 figures, submitted to Phys. Rev. A, RevTeX
sourc
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
Simultaneous dual-color and dual-polarization imaging of single molecules
Biological and Soft Matter Physic
Carbon nanotubes adhesion and nanomechanical behavior from peeling force spectroscopy
Applications based on Single Walled Carbon Nanotube (SWNT) are good example
of the great need to continuously develop metrology methods in the field of
nanotechnology. Contact and interface properties are key parameters that
determine the efficiency of SWNT functionalized nanomaterials and nanodevices.
In this work we have taken advantage of a good control of the SWNT growth
processes at an atomic force microscope (AFM) tip apex and the use of a low
noise (1E-13 m/rtHz) AFM to investigate the mechanical behavior of a SWNT
touching a surface. By simultaneously recording static and dynamic properties
of SWNT, we show that the contact corresponds to a peeling geometry, and
extract quantities such as adhesion energy per unit length, curvature and
bending rigidity of the nanotube. A complete picture of the local shape of the
SWNT and its mechanical behavior is provided
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
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
- …