1,162 research outputs found
Nonlinear acoustic theory for thin porous sheets
Nonlinear method for predicting acoustic properties of thin porous sheet
Experimental feasibility of investigating acoustic waves in Couette flow with entropy and pressure gradients
The feasibility is discussed for an experimental program for studying the behavior of acoustic wave propagation in the presence of strong gradients of pressure, temperature, and flow. Theory suggests that gradients effects can be experimentally observed as resonant frequency shifts and mode shape changes in a waveguide. A convenient experimental geometry for such experiments is the annular region between two co-rotating cylinders. Radial temperature gradients in a spinning annulus can be generated by differentially heating the two cylinders via electromagnetic induction. Radial pressure gradients can be controlled by varying the cylinder spin rates. Present technology appears adequate to construct an apparatus to allow independent control of temperature and pressure gradients. A complicating feature of a more advanced experiment, involving flow gradients, is the requirement for independently controlled cylinder spin rates. Also, the boundary condition at annulus terminations must be such that flow gradients are minimally disturbed. The design and construction of an advanced apparatus to include flow gradients will require additional technology development
Mobile satellite service in the United States
Mobile satellite service (MSS) has been under development in the United States for more than two decades. The service will soon be provided on a commercial basis by a consortium of eight U.S. companies called the American Mobile Satellite Consortium (AMSC). AMSC will build a three-satellite MSS system that will offer superior performance, reliability and cost effectiveness for organizations requiring mobile communications across the U.S. The development and operation of MSS in North America is being coordinated with Telesat Canada and Mexico. AMSC expects NASA to provide launch services in exchange for capacity on the first AMSC satellite for MSAT-X activities and for government demonstrations
The AMSC mobile satellite system
The American Mobile Satellite Consortium (AMSC) Mobile Satellite Service (MSS) system is described. AMSC will use three multi-beam satellites to provide L-band MSS coverage to the United States, Canada and Mexico. The AMSC MSS system will have several noteworthy features, including a priority assignment processor that will ensure preemptive access to emergency services, a flexible SCPC channel scheme that will support a wide diversity of services, enlarged system capacity through frequency and orbit reuse, and high effective satellite transmitted power. Each AMSC satellite will make use of 14 MHz (bi-directional) of L-band spectrum. The Ku-band will be used for feeder links
The structure and mechanistic impact of carbon deposits in dehydrogenation reactions
The catalytic dehydrogenation (DH) and oxidative dehydrogenation (ODH) of light alkanes is widely studied as a route to the formation of alkenes and di-alkenes, important precursor molecules for synthetic rubbers, plastics and a variety of other products [1-4]. Recent studies have focused on the non-oxidative DH of butane over alumina-supported vanadia catalysts [5-7]. In the present work, we provide a detailed understanding of both the role and structure of coke deposited on VOx/Al2O3 during reaction. A range of characterisation techniques have been employed including the first application of terahertz time domain spectroscopy (THz-TDS) to the study of coke. Complementary THz-TDS characterisation of carbonaceous materials including carbon nanofibres (CNFs) has also been conducted
The role and structure of carbonaceous materials in dehydrogenation reactions
The catalytic dehydrogenation (DH) and oxidative dehydrogenation (ODH) of light alkanes is widely studied as a route to the formation of alkenes and di-alkenes, important precursor molecules for synthetic rubbers, plastics and a variety of other products [1,2]. Recent studies have focused on the non-oxidative DH of butane over alumina-supported vanadia catalysts [3-5]. In the present work, we provide a detailed understanding of both the role and structure of coke deposited on VOx/Al2O3 during reaction. A range of characterisation techniques have been employed including the first application of terahertz time domain spectroscopy (THz-TDS) to the study of coke. Complementary THz-TDS characterisation of carbonaceous materials including carbon nanofibres (CNFs) has also been conducted. For such materials THz-TDS spectra can be correlated with their catalytic performance in the oxidative dehydrogenation of ethylbenzene to form styrene
Cerenkov radiation and scalar stars
We explore the possibility that a charged particle moving in the
gravitational field generated by a scalar star could radiate energy via a
recently proposed gravitational \v{C}erenkov mechanism. We numerically prove
that this is not possible for stable boson stars. We also show that soliton
stars could have \v{C}erenkov radiation for particular values of the boson
mass, although diluteness of the star grows and actual observational
possibility decreases for the more usually discussed boson masses. These
conclusions diminish, although do not completely rule out, the observational
possibility of actually detecting scalar stars using this mechanism, and lead
us to consider other forms, like gravitational lensing.Comment: Accepted for publication in Class. Quantum Gra
Subtumoral analysis of PRINT nanoparticle distribution reveals targeting variation based on cellular and particle properties
AbstractThe biological activity of nanoparticle-directed therapies critically depends on cellular targeting. We examined the subtumoral fate of Particle Replication in Non-Wetting Templates (PRINT) nanoparticles in a xenografted melanoma tumor model by multi-color flow cytometry and in vivo confocal tumor imaging. These approaches were compared with the typical method of whole-organ quantification by radiolabeling. In contrast to radioactivity based detection which demonstrated a linear dose-dependent accumulation in the organ, flow cytometry revealed that particle association with cancer cells became dose-independent with increased particle doses and that the majority of the nanoparticles in the tumor were associated with cancer cells despite a low fractional association. In vivo imaging demonstrated an inverse relationship between tumor cell association and other immune cells, likely macrophages. Finally, variation in particle size nonuniformly affected subtumoral association. This study demonstrates the importance of subtumoral targeting when assessing nanoparticle activity within tumors.From the Clinical EditorParticle Replication in Non-Wetting Templates (PRINT) technology allows the production of nanoparticles with uniform size. The authors in the study utilized PRINT-produced nanoparticles to investigate specific tumor uptake by multi-color flow cytometry and in vivo confocal tumor imaging. This approach allowed further in-depth correlation between nanoparticle properties and tumor cells and should improve future design
The visibility of IQHE at sharp edges: Experimental proposals based on interactions and edge electrostatics
The influence of the incompressible strips on the integer quantized Hall
effect (IQHE) is investigated, considering a cleaved-edge overgrown (CEO)
sample as an experimentally realizable sharp edge system. We propose a set of
experiments to clarify the distinction between the large-sample limit when bulk
disorder defines the IQHE plateau width and the small-sample limit smaller than
the disorder correlation length, when self-consistent edge electrostatics
define the IQHE plateau width. The large-sample or bulk QH regime is described
by the usual localization picture, whereas the small-sample or edge regime is
discussed within the compressible/incompressible strips picture, known as the
screening theory of QH edges. Utilizing the unusually sharp edge profiles of
the CEO samples, a Hall bar design is proposed to manipulate the edge potential
profile from smooth to extremely sharp. By making use of a side-gate
perpendicular to the two dimensional electron system, it is shown that the
plateau widths can be changed or even eliminated altogether. Hence, the
visibility of IQHE is strongly influenced when adjusting the edge potential
profile and/or changing the dc current direction under high currents in the
non-linear transport regime. As a second investigation, we consider two
different types of ohmic contacts, namely highly transmitting (ideal) and
highly reflecting (non-ideal) contacts. We show that if the injection contacts
are non-ideal, however still ohmic, it is possible to measure directly the
non-quantized transport taking place at the bulk of the CEO samples. The
results of the experiments we propose will clarify the influence of the edge
potential profile and the quality of the contacts, under quantized Hall
conditions.Comment: Substantially revised version of manuscript arXiv:0906.3796v1,
including new figures et
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