75,651 research outputs found
Ultra-low Cost THz Short-range Wireless Link
This paper demonstrates an ultra-low cost THz system for implementing a short-range wireless communications link in the far/mid-infrared parts of the electromagnetic spectrum. The basic prototype front-end hardware is deliberately kept very simple; based around miniature incandescent light bulbs, THz filters and pyroelectric infrared sensors. While only a low data rate has been experimentally demonstrated so far, this does not represent a fundamental limitation, as a number of technological enhancements are possible. It is believed that this “THz torch” technology has its niche in ubiquitous security applications that do not require high data rates or large distance operation (e.g. secure RFID, smart key fobs and remote controls).Accepted versio
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Thermomechanical Reliability Challenges For 3D Interconnects With Through-Silicon Vias
Continual scaling of on-chip wiring structures has brought significant challenges for materials and processes beyond the 32 nm technology node in microelectronics. Recently threedimensional (3-D) integration with through-silicon-vias (TSVs) has emerged as an effective solution to meet the future interconnect requirement. Among others, thermo-mechanical reliability is a key concern for the development of TSV structures used in die stacking as 3-D interconnects. This paper examines the effects of thermally induced stresses on interfacial reliability of TSV structures. First, three-dimensional distribution of the thermal stress near the TSV and the wafer surface is analyzed. Using a linear superposition method, a semi-analytic solution is developed for a simplified structure consisting of a single TSV embedded in a silicon (Si) wafer. The solution is verified for relatively thick wafers by comparing to numerical results From finite element analysis (FEA). The stress analysis suggests interfacial delamination as a potential failure mechanism for the TSV structure. An analytical solution is then obtained for the steady-state energy release rate as the upper bound for the interfacial fracture driving force, while the effect of crack length is evaluated numerically by FEA. With these results, the effects of the TSV dimensions (e.g., via diameter and wafer thickness) on the interfacial reliability are elucidated. Furthermore, the effects of via material properties are discussed.Aerospace Engineerin
New Spinor Field Realizations of the Non-Critical String
We investigate the new spinor field realizations of the algebra,
making use of the fact that the algebra can be linearized by the
addition of a spin-1 current. We then use these new realizations to build the
nilpotent Becchi-Rouet-Stora--Tyutin (BRST) charges of the spinor non-critical
string.Comment: 8 pages, no figures, revtex4 style, accepted by Chin. Phys. Let
Dynamical properties of dipolar Fermi gases
We investigate dynamical properties of a one-component Fermi gas with
dipole-dipole interaction between particles. Using a variational function based
on the Thomas-Fermi density distribution in phase space representation, the
total energy is described by a function of deformation parameters in both real
and momentum space. Various thermodynamic quantities of a uniform dipolar Fermi
gas are derived, and then instability of this system is discussed. For a
trapped dipolar Fermi gas, the collective oscillation frequencies are derived
with the energy-weighted sum rule method. The frequencies for the monopole and
quadrupole modes are calculated, and softening against collapse is shown as the
dipolar strength approaches the critical value. Finally, we investigate the
effects of the dipolar interaction on the expansion dynamics of the Fermi gas
and show how the dipolar effects manifest in an expanded cloud.Comment: 14 pages, 8 figures, submitted to New J. Phy
Isothermal Shock Formation in Non-Equatorial Accretion Flows around Kerr Black Holes
We explore isothermal shock formation in non-equatorial, adiabatic accretion
flows onto a rotating black hole, with possible application to some active
galactic nuclei (AGNs). The isothermal shock jump conditions as well as the
regularity condition, previously developed for one-dimensional (1D) flows in
the equatorial plane, are extended to two-dimensional (2D), non-equatorial
flows, to explore possible geometrical effects. The basic hydrodynamic
equations with these conditions are self-consistently solved in the context of
general relativity to explore the formation of stable isothermal shocks. We
find that strong shocks are formed in various locations above the equatorial
plane, especially around a rapidly-rotating black hole with the prograde flows
(rather than a Schwarzschild black hole). The retrograde flows are generally
found to develop weaker shocks. The energy dissipation across the shock in the
hot non-equatorial flows above the cooler accretion disk may offer an
attractive illuminating source for the reprocessed features, such as the iron
fluorescence lines, which are often observed in some AGNs.Comment: 22 pages with 11 figures, presented at 5th international conference
on high energy density laboratory astrophysics in Tucson, Arizona. accepted
to Ap
Mass Outflows from Dissipative Shocks in Hot Accretion Flows
We consider stationary, axisymmetric hydrodynamic accretion flows in Kerr
geometry. As a plausible means of efficiently separating a small population of
nonthermal particles from the bulk accretion flows, we investigate the
formation of standing dissipative shocks, i.e. shocks at which fraction of the
energy, angular momentum and mass fluxes do not participate in the shock
transition of the flow that accretes onto the compact object but are lost into
collimated (jets) or uncollimated (winds) outflows. The mass loss fraction (at
a shock front) is found to vary over a wide range (0 - 95%) depending on flow's
angular momentum and energy. On the other hand, the associated energy loss
fraction appears to be relatively low (<1%) for a flow onto a non-rotating
black hole case, whereas the fraction could be an order of magnitude higher
(<10%) for a flow onto a rapidly-rotating black hole. By estimating the escape
velocity of the outflowing particles with a mass-accretion rate relevant for
typical active galactic nuclei, we find that nearly 10% of the accreting mass
could escape to form an outflow in a disk around a non-rotating black hole,
while as much as 50% of the matter may contribute to outflows in a disk around
a rapidly-rotating black hole. In the context of disk-jet paradigm, our model
suggests that shock-driven outflows from accretion can occur in regions not too
far from a central engine. Our results imply that a shock front under some
conditions could serve as a plausible site where (nonthermal) seed particles of
the outflows (jets/winds) are efficiently decoupled from bulk accretion.Comment: 25 pages, 10 black&white figures, Accepted to Ap
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