2,797 research outputs found
Electrostatically controlled heat shutter
A heat transfer assembly for conducting thermal energy is described. The assembly includes a hermetically sealed container enclosing a quantity of inert gas such as nitrogen. Two opposed walls of the container have high thermal conducting characteristics while the connecting walls have low thermal conducting characteristics. Electrodes are positioned adjacent to the high thermal conducing walls and biased relative to the conducting walls to a corona potential for creating an ionic gas wind which must contact the conducting walls to be neutralized. The contact of the gas molecules permits the maximum thermal energy transfer between the walls. Baffles can be positioned adjacent to the electrodes to regulate gas flow between the high thermal conducting surfaces
Disconjugacy of a second order linear differential equation and periodic solutions
The present paper is devoted to a new criterion for disconjugacy of a second
order linear differential equation. Unlike most of the classical sufficient
conditions for disconjugacy, our criterion does not involve assumptions on the
smallness of the coefficients of the equation. We compare our criterion with
several known criteria for disconjugacy, for which we provide detailed proofs,
and discuss the applications of the property of disconjugacy to the problem of
factorization of linear ordinary differential operators, and to the proof of
the generalized Rolle's theorem. The paper is self-contained, and may serve as
a brief introduction to theory of disconjugacy of a second order linear
differential equation
Heated bimetal strip prevents damage of bearings by vibration
Strip of bimetal is shaped as split ring; when properly fabricated from thin sheet, width of strip increases when it is heated. When width of strip increases, outer races are forced apart, thus pressing balls tightly against inner races. Strip applies axial load to bearing, amount of load being function of temperature to which strip is heated
On uniform continuous dependence of solution of Cauchy problem on a parameter
Suppose that an -dimensional Cauchy problem \frac{dx}{dt}=f(t,x,\mu) (t
\in I, \mu \in M), x(t_0)=x^0 satisfies the conditions that guarantee
existence, uniqueness and continuous dependence of solution x(t,t_0,\mu) on
parameter \mu in an open set M. We show that if one additionally requires that
family \{f(t,x,\cdot)\}_{(t,x)} is equicontinuous, then the dependence of
solution x(t,t_0,\mu) on parameter \mu \in M is uniformly continuous.
An analogous result for a linear n \times n-dimensional Cauchy problem
\frac{dX}{dt}=A(t,\mu)X+\Phi(t,\mu) (t \in I, \mu \in M), X(t_0,\mu)=X^0(\mu)
is valid under the assumption that the integrals
\int_I\|A(t,\mu_1)-A(t,\mu_2)\|dt and \int_I \|\Phi(t,\mu_1)-\Phi(t,\mu_2)\|dt
can be made smaller than any given constant (uniformly with respect to \mu_1,
\mu_2 \in M) provided that \|\mu_1-\mu_2\| is sufficiently small
Distributions with dynamic test functions and multiplication by discontinuous functions
As follows from the Schwartz Impossibility Theorem, multiplication of two
distributions is in general impossible. Nevertheless, often one needs to
multiply a distribution by a discontinuous function, not by an arbitrary
distribution. In the present paper we construct a space of distributions where
the general operation of multiplication by a discontinuous function is defined,
continuous, commutative, associative and for which the Leibniz product rule
holds. In the new space of distributions, the classical delta-function
extends to a family of delta-functions ,
dependent on the \textit{shape} . We show that the various known
definitions of the product of the Heaviside function and the delta-function in
the classical space of distributions become particular cases of
the multiplication in the new space of distributions, and provide the
applications of the new space of distributions to the ordinary differential
equations which arise in optimal control theory. Also, we compare our approach
of the Schwartz distribution theory with the approach of the Colombeau
generalized functions algebra, where the general operation of multiplication of
two distributions is defined
Shear flow-interchange instability in nightside magnetotail causes auroral beads as a signature of substorm onset
A geometric wedge model of the near-earth nightside plasma sheet is used to
derive a wave equation for low frequency shear flow-interchange waves which
transmit sheared zonal flows along magnetic flux tubes
towards the ionosphere. Discrepancies with the wave equation result used in
Kalmoni et al. (2015) for shear flow-ballooning instability are discussed. The
shear flow-interchange instability appears to be responsible for substorm
onset. The wedge wave equation is used to compute rough expressions for
dispersion relations and local growth rates in the midnight region of the
nightside magnetotail where the instability develops, forming the auroral beads
characteristic of geomagnetic substorm onset. Stability analysis for the shear
flow-interchange modes demonstrates that nonlinear analysis is necessary for
quantitatively accurate results and determines the spatial scale on which the
instability varies
Contra Epstein, Good Explanations Predict
Epstein has argued that an explanation\'s capacity to make predictions should play a minor role in its evaluation . This view contradicts centuries of scientific practice and, at least, decades of philosophy of science. We argue that the view is not only unfounded but seems to arise from a mistaken fear that ABM models are in need of defense against the criticism that they don\'t necessarily forecast events in the natural or social world.ABM, Agent Based Model, Modeling, Prediction, Explanation, Philosophy of Science
Using CMOS Sensors in a Cellphone for Gamma Detection and Classification
The CMOS camera found in many cellphones is sensitive to ionized electrons.
Gamma rays penetrate into the phone and produce ionized electrons that are then
detected by the camera. Thermal noise and other noise needs to be removed on
the phone, which requires an algorithm that has relatively low memory and
computational requirements. The continuous high-delta algorithm described fits
those requirements. Only a small fraction of the energy of even the electron is
deposited in the camera sensor, so direct methods of measuring the energy
cannot be used. The fraction of groups of lit up pixels that are lines is
correlated with the energy of the gamma rays. This correlation under certain
conditions allows limited low resolution energy resolution to be performed
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