1,654 research outputs found
Exploiting pattern transformation to tune phononic band gaps in a two-dimensional granular crystal
The band structure of a two-dimensional granular crystal composed of silicone rubber and polytetrafluoroethylene (PTFE) cylinders is investigated numerically. This system was previously shown to undergo a pattern transformation with uniaxial compression by Göncü et al. [Soft Matter 7, 2321 (2011)]. The dispersion relations of the crystal are computed at different levels of deformation to demonstrate the tunability of the band structure, which is strongly affected by the pattern transformation that induces new band gaps. Replacement of PTFE particles with rubber ones reveals that the change of the band structure is essentially governed by pattern transformation rather than particles¿ mechanical properties
Deep Energy Retrofits Using the Integrative Design Process: Are they Worth the Cost
The McKinsey Global Initiative identified existing building retrofits as an integral component to achieve a 75% reduction in greenhouse gas emissions in the United Sates by 2050 (Fluhrer, Maurer, & Deshmukh 2010). However, this will require energy efficiency retrofits for existing buildings to be deployed more frequently and achieve higher energy savings on average. Deep Energy Retrofits using the Integrative Design Process can result in 30-60%+ energy savings in office buildings. Because Deep Energy Retrofits require higher upfront capital costs, in an economy still recovering from the economic downturn, financial decision makers may not be inclined to invest more capital solely on the basis of higher energy savings. In this paper, Deep Energy Retrofit case studies, research papers, and retrofit guides were examined to answer the question: are deep energy retrofits financially viable, and if so, under what conditions. Utility cost savings, avoided capital costs, as well as additional benefits, like increased reputation, environmental health and enhanced comfort of the building are ways in which Deep Energy Retrofits can be cost-effective; and in some cases profitable for the financial decision maker or building owner. Deep Energy Retrofits using the integrative Design Process present a low-cost and effective strategy to reduce GHG emissions and help aid the US in climate stabilization efforts
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Generation of Porous Structures Using Fused Deposition
The Fused Deposition Modeling process uses hardware and software machine-level
language that are very similar to that of a pen-plotter. Consequently, the·use of patterns with
poly-lines as basic geometric features, instead of the current method based on filled polygons
(monolithic models), can increase its efficiency.
In the current study, various toolpath planning methods have been developed to fabricate
porous structures. Computational domain decomposition methods can be applied to the physical
or to slice-level domains to generate structured and unstructured grids. Also, textures can be
created using periodic tiling of the layer with unit cells (squares, honeycombs, etc). Methods
'based on curves include fractal space filling curves and.change of effective road width Within a
layer or within a continuous curve. Individual phases can also be placed in binary compositions.
In present investigation, a custom software has been developed and implemented to
generate build files (SML) and slice files (SSL) for the above-mentioned structures, demonstrating the efficient control ofthe size, shape, and distribution ofporosity.Mechanical Engineerin
Feedback control of trapped coherent atomic ensembles
We demonstrate how to use feedback to control the internal states of trapped
coherent ensembles of two-level atoms, and to protect a superposition state
against the decoherence induced by a collective noise. Our feedback scheme is
based on weak optical measurements with negligible back-action and coherent
microwave manipulations. The efficiency of the feedback system is studied for a
simple binary noise model and characterized in terms of the trade-off between
information retrieval and destructivity from the optical probe. We also
demonstrate the correction of more general types of collective noise. This
technique can be used for the operation of atomic interferometers beyond the
standard Ramsey scheme, opening the way towards improved atomic sensors.Comment: 9 pages, 6 figure
Near-Infrared Photometry of the High-Redshift Quasar RDJ030117+002025: Evidence for a Massive Starburst at z=5.5
With a redshift of z=5.5 and an optical blue magnitude M_B ~ -24.2 mag (~4.5
10^12 L_sun), RDJ030117+002025 is the most distant optically faint (M_B > -26
mag) quasar known. MAMBO continuum observations at lambda=1.2 mm (185
micrometer rest-frame) showed that this quasar has a far-IR luminosity
comparable to its optical luminosity. We present near-infrared J- and K-band
photometry obtained with NIRC on the Keck I telescope, tracing the slope of the
rest frame UV spectrum of this quasar. The observed spectral index is close to
the value of alpha_nu ~ -0.44 measured in composite spectra of optically-bright
SDSS quasars. It thus appears that the quasar does not suffer from strong dust
extinction, which further implies that its low rest-frame UV luminosity is due
to an intrinsically-faint AGN. The FIR to optical luminosity ratio is then much
larger than that observed for the more luminous quasars, supporting the
suggestion that the FIR emission is not powered by the AGN but by a massive
starburst.Comment: 6 pages, APJ in pres
Spin-squeezing and Dicke state preparation by heterodyne measurement
We investigate the quantum non-demolition (QND) measurement of an atomic
population based on a heterodyne detection and show that the induced
back-action allows to prepare both spin-squeezed and Dicke states. We use a
wavevector formalism to describe the stochastic process of the measurement and
the associated atomic evolution. Analytical formulas of the atomic distribution
momenta are derived in the weak coupling regime both for short and long time
behavior, and they are in good agreement with those obtained by a Monte-Carlo
simulation. The experimental implementation of the proposed heterodyne
detection scheme is discussed. The role played in the squeezing process by the
spontaneous emission is considered
Thermodynamics of Dyonic Lifshitz Black Holes
Black holes with asymptotic anisotropic scaling are conjectured to be gravity
duals of condensed matter system close to quantum critical points with
non-trivial dynamical exponent z at finite temperature. A holographic
renormalization procedure is presented that allows thermodynamic potentials to
be defined for objects with both electric and magnetic charge in such a way
that standard thermodynamic relations hold. Black holes in asymptotic Lifshitz
spacetimes can exhibit paramagnetic behavior at low temperature limit for
certain values of the critical exponent z, whereas the behavior of AdS black
holes is always diamagnetic.Comment: 26 pages, 4 figure
Large N gauge theories and topological cigars
We analyze the conjectured duality between a class of double-scaling limits
of a one-matrix model and the topological twist of non-critical superstring
backgrounds that contain the N=2 Kazama-Suzuki SL(2)/U(1) supercoset model. The
untwisted backgrounds are holographically dual to double-scaled Little String
Theories in four dimensions and to the large N double-scaling limit of certain
supersymmetric gauge theories. The matrix model in question is the auxiliary
Dijkgraaf-Vafa matrix model that encodes the F-terms of the above
supersymmetric gauge theories. We evaluate matrix model loop correlators with
the goal of extracting information on the spectrum of operators in the dual
non-critical bosonic string. The twisted coset at level one, the topological
cigar, is known to be equivalent to the c=1 non-critical string at self-dual
radius and to the topological theory on a deformed conifold. The spectrum and
wavefunctions of the operators that can be deduced from the matrix model
double-scaling limit are consistent with these expectations.Comment: 34 page
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