14,757 research outputs found
Theoretical investigation of liquid water injection into the shock layer of a reentry vehicle
Mathematical model for flow field of liquid spray injected into supersonic air streaming past blunt bod
Analytic Determination of the Critical Coupling for Oscillators in a Ring
We study a model of coupled oscillators with bidirectional first nearest
neighbours coupling with periodic boundary conditions. We show that a stable
phase-locked solution is decided by the oscillators at the borders between the
major clusters, which merge to form a larger one of all oscillators at the
stage of complete synchronization. We are able to locate these four oscillators
as well as the size of major clusters in the vicinity of the stage of full
synchronization which we show to depend only on the set of initial frequencies.
Using the method presented here, we are able to obtain an analytic form of the
critical coupling, at which the complete synchronization state occurs.Comment: 5 pages and 3 figure
Frequency reconfigurable patch antenna for 4G LTE applications
A compact printed multi-band frequency reconfigurable patch antenna for 4G LTE applications is presented in this paper (50 x 60 x 1.6 mm3). The antenna consists of W-shaped and Inverted-U shaped patch lines connected in a Tree-shape on the front side of the antenna. The back-side of the antenna contains a 90Ā°-tilted T-shaped strip connected with an Inverted-L shaped strip which is shorted with a patch on the front side for increasing the electrical length to cover lower frequency bands. Frequency reconfigurability is achieved by inserting three switches i.e., PIN diodes. The most critical part of this work is the designing of RLC-based DC line circuits for providing the DC biasing to the PIN diodes used as switches and inserting them at optimum locations. This antenna is reconfigurable among eight different 4G LTE frequency bands including 0.9 GHz, 1.4 GHz, 1.5 GHz, 1.6 GHz, 1.7 GHz, 1.8 GHz, 2.6 GHz, 3.5 GHz and WLAN band 2.5 GHz. The antenna exhibits different radiation patterns having a different direction of peak gain at different frequencies and for different switching combinations. The antenna is simulated with CST, and a prototype is fabricated to compare the measured and simulated results with good accuracy
Collective Modes of Massive Dirac Fermions in Armchair Graphene Nanoribbons
We report the plasmon dispersion characteristics of intrinsic and extrinsic
armchair graphene nanoribbons of atomic width N = 5 using a p_z-orbital tight
binding model with third-nearest-neighbor (3nn) coupling. The coupling
parameters are obtained by fitting the 3nn dispersions to that of an extended
Huckel theory. The resultant massive Dirac Fermion system has a band gap E_g
\approx 64 meV. The extrinsic plasmon dispersion relation is found to approach
a common dispersion curve as the chemical potential increases, whereas
the intrinsic plasmon dispersion relation is found to have both energy and
momentum thresholds. We also report an analytical model for the extrinsic
plasmon group velocity in the q \rightarrow 0 limit
Dynamics and Long-Run Structure in U.S. Meat Demand
ļæ½Empirical analysis, based on a general dynamic Almost Ideal Demand System, shows the commonly used autoregressive and partial adjustment processes are restrictive to meal demand data. This study derives a linear specification in levels form to investigate dynamics in a general framework. Merging a long-run steady state structure with short-run dynamics results in consistent and robust long-run demand elasticities.
Rearrangements and Dilatancy for Sheared Dense Materials
Constitutive equations are proposed for dense materials, based on the
identification of two types of free-volume activated rearrangements associated
to shear and compaction. Two situations are studied: the case of an amorphous
solid in a stress-strain test, and the case of a lubricant in tribology test.
Varying parameters, strain softening, shear thinning, and stick-slip motion can
be observed.Comment: 4 pages, 3 figure
Characterizing and Predicting Email Deferral Behavior
Email triage involves going through unhandled emails and deciding what to do
with them. This familiar process can become increasingly challenging as the
number of unhandled email grows. During a triage session, users commonly defer
handling emails that they cannot immediately deal with to later. These deferred
emails, are often related to tasks that are postponed until the user has more
time or the right information to deal with them. In this paper, through
qualitative interviews and a large-scale log analysis, we study when and what
enterprise email users tend to defer. We found that users are more likely to
defer emails when handling them involves replying, reading carefully, or
clicking on links and attachments. We also learned that the decision to defer
emails depends on many factors such as user's workload and the importance of
the sender. Our qualitative results suggested that deferring is very common,
and our quantitative log analysis confirms that 12% of triage sessions and 16%
of daily active users had at least one deferred email on weekdays. We also
discuss several deferral strategies such as marking emails as unread and
flagging that are reported by our interviewees, and illustrate how such
patterns can be also observed in user logs. Inspired by the characteristics of
deferred emails and contextual factors involved in deciding if an email should
be deferred, we train a classifier for predicting whether a recently triaged
email is actually deferred. Our experimental results suggests that deferral can
be classified with modest effectiveness. Overall, our work provides novel
insights about how users handle their emails and how deferral can be modeled
Zero Temperature Insulator-Metal Transition in Doped Manganites
We study the transition at T=0 from a ferromagnetic insulating to a
ferromagnetic metallic phase in manganites as a function of hole doping using
an effective low-energy model Hamiltonian proposed by us recently. The model
incorporates the quantum nature of the dynamic Jahn-Teller(JT) phonons strongly
coupled to orbitally degenerate electrons as well as strong Coulomb correlation
effects and leads naturally to the coexistence of localized (JT polaronic) and
band-like electronic states. We study the insulator-metal transition as a
function of doping as well as of the correlation strength U and JT gain in
energy E_{JT}, and find, for realistic values of parameters, a ground state
phase diagram in agreement with experiments. We also discuss how several other
features of manganites as well as differences in behaviour among manganites can
be understood in terms of our model.Comment: To be published in Europhysics Letter
- ā¦