15,084 research outputs found
Nanofibers in face masks and respirators to provide better protection
A facemask is a loose-fitting, disposable device that creates a physical barrier between the mouth and nose of the wearer and potential contaminants in the immediate environment. They are generally labelled as surgical, isolation, dental or medical procedure masks. On the other hand, respirators are personal air purifiers. They are designed to protect the wearer from inhaling dangerous substances such as toxic chemicals and infectious particles. Respirators are designed to help reduce the wearer's respiratory exposure to airborne contaminants such as particles that are small enough to be inhaled - particles less than 100 microns (μm) in size. A face masks or a respirator consist entirely or substantially of filter material or comprises a face piece in which the main filter(s) form an inseparable part of the device. Nanofibers could be the key elements for filter materials in face masks or respirators. They have a very high surface area per unit mass that enhances capture efficiency and other surface area-dependent phenomena that may be engineered into the fiber surfaces (such as catalysis or ion exchange). They could enhance filter performance for capture of naturally occurring nanoparticles such as viruses, as well as micron-sized particles such as bacteria or man-made particles such as soot from diesel exhaust. © Published under licence by IOP Publishing Ltd
Improved version of the eikonal model for absorbing spherical particles
We present a new expression of the scattering amplitude, valid for spherical
absorbing objects, which leads to an improved version of the eikonal method
outside the diffraction region. Limitations of this method are discussed and
numerical results are presented and compared successfully with the Mie theory.Comment: 7 pages, postscript figures available on cpt.univ-mrs.fr, to appear
in J. Mod. Optic
Effect of picosecond strain pulses on thin layers of the ferromagnetic semiconductor (Ga,Mn)(As,P)
The effect of picosecond acoustic strain pulses (ps-ASP) on a thin layer of
(Ga,Mn)As co-doped with phosphorus was probed using magneto-optical Kerr effect
(MOKE). A transient MOKE signal followed by low amplitude oscillations was
evidenced, with a strong dependence on applied magnetic field, temperature and
ps-ASP amplitude. Careful interferometric measurement of the layer's thickness
variation induced by the ps-ASP allowed us to model very accurately the
resulting signal, and interpret it as the strain modulated reflectivity
(differing for probe polarizations), independently from dynamic
magnetization effects.Comment: 6 pages, 5 figure
Sub-Terahertz Monochromatic Transduction with Semiconductor Acoustic Nanodevices
We demonstrate semiconductor superlattices or nanocavities as narrow band
acoustic transducers in the sub-terahertz range. Using picosecond ultrasonics
experiments in the transmission geometry with pump and probe incident on
opposite sides of the thick substrate, phonon generation and detection
processes are fully decoupled. Generating with the semiconductor device and
probing on the metal, we show that both superlattices and nanocavities generate
spectrally narrow wavepackets of coherent phonons with frequencies in the
vicinity of the zone center and time durations in the nanosecond range,
qualitatively different from picosecond broadband pulses usually involved in
picosecond acoustics with metal generators. Generating in the metal and probing
on the nanoacoustic device, we furthermore evidence that both nanostructured
semiconductor devices may be used as very sensitive and spectrally selective
detectors
Sound velocity and absorption measurements under high pressure using picosecond ultrasonics in diamond anvil cell. Application to the stability study of AlPdMn
We report an innovative high pressure method combining the diamond anvil cell
device with the technique of picosecond ultrasonics. Such an approach allows to
accurately measure sound velocity and attenuation of solids and liquids under
pressure of tens of GPa, overcoming all the drawbacks of traditional
techniques. The power of this new experimental technique is demonstrated in
studies of lattice dynamics, stability domain and relaxation process in a
metallic sample, a perfect single-grain AlPdMn quasicrystal, and rare gas, neon
and argon. Application to the study of defect-induced lattice stability in
AlPdMn up to 30 GPa is proposed. The present work has potential for application
in areas ranging from fundamental problems in physics of solid and liquid
state, which in turn could be beneficial for various other scientific fields as
Earth and planetary science or material research
Finiteness of cominuscule quantum K-theory
The product of two Schubert classes in the quantum K-theory ring of a
homogeneous space X = G/P is a formal power series with coefficients in the
Grothendieck ring of algebraic vector bundles on X. We show that if X is
cominuscule, then this power series has only finitely many non-zero terms. The
proof is based on a geometric study of boundary Gromov-Witten varieties in the
Kontsevich moduli space, consisting of stable maps to X that take the marked
points to general Schubert varieties and whose domains are reducible curves of
genus zero. We show that all such varieties have rational singularities, and
that boundary Gromov-Witten varieties defined by two Schubert varieties are
either empty or unirational. We also prove a relative Kleiman-Bertini theorem
for rational singularities, which is of independent interest. A key result is
that when X is cominuscule, all boundary Gromov-Witten varieties defined by
three single points in X are rationally connected.Comment: 16 pages; proofs slightly improved; explicit multiplications in
QK(Cayley plane) from v1 no longer necessar
Projected Gromov-Witten varieties in cominuscule spaces
A projected Gromov-Witten variety is the union of all rational curves of
fixed degree that meet two opposite Schubert varieties in a homogeneous space X
= G/P. When X is cominuscule we prove that the map from a related Gromov-Witten
variety is cohomologically trivial. This implies that all (3 point, genus zero)
K-theoretic Gromov-Witten invariants of X are determined by the projected
Gromov-Witten varieties, which extends an earlier result of Knutson, Lam, and
Speyer. Our proof uses that any projected Gromov-Witten variety in a
cominuscule space is also a projected Richardson variety.Comment: 13 page
Updated results on prototype chalcogenide fibers for 10-um wavefront spatial filtering
The detection of terrestrial planets by Darwin/TPF missions will require
extremely high quality wavefronts. Single-mode fibers have proven to be
powerful beam cleaning components in the near-infrared, but are currently not
available in the mid-infrared where they would be critically needed for
Darwin/TPF. In this paper, we present updated measurements on the prototype
chalcogenide fibers we are developing for the purpose of mid-infrared spatial
filtering. We demonstrate the guiding property of our 3rd generation component
and we characterize its filtering performances on a 4 mm length: the far-field
radiation pattern matches a Gaussian profile at the level of 3% rms and 13%
pk-pk.Comment: 4 pages, 5 figures, to appear in the proceedings of the conference
"Toward Other Earths, Darwin/TPF and the search for extrasolar terrestrial
planets", held in Heidelberg, Germany, 22-25 April 2003, ESA SP-53
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