578 research outputs found
Speed control with low armature loss for very small sensorless brushed DC motors
A method for speed control of brushed dc motors is presented. It is particularly applicable to motors with armatures of less than 1 cm3. Motors with very small armatures are difficult to control using the usual pulsewidth-modulation (PWM) approach and are apt to overheat if so driven. The technique regulates speed via the back electromotive force but does not require current-discontinuous drives. Armature heating in small motors under PWM drive is explained and quantified. The method is verified through simulation and measurement. Control is improved, and armature losses are minimized. The method can expect to find application in miniature mechatronic equipment
Phase Separation in Binary Fluid Mixtures with Continuously Ramped Temperature
We consider the demixing of a binary fluid mixture, under gravity, which is
steadily driven into a two phase region by slowly ramping the temperature. We
assume, as a first approximation, that the system remains spatially isothermal,
and examine the interplay of two competing nonlinearities. One of these arises
because the supersaturation is greatest far from the meniscus, creating
inversion of the density which can lead to fluid motion; although isothermal,
this is somewhat like the Benard problem (a single-phase fluid heated from
below). The other is the intrinsic diffusive instability which results either
in nucleation or in spinodal decomposition at large supersaturations.
Experimental results on a simple binary mixture show interesting oscillations
in heat capacity and optical properties for a wide range of ramp parameters. We
argue that these oscillations arise under conditions where both nonlinearities
are important
КЕРАМІКА КАМ’ЯНСЬКОЇ СІЧІ (1709-1711; 1728-1734 рр.): ІСТОРІЯ, ФУНКЦІОНАЛЬНІ ОСОБЛИВОСТІ, СЕМАНТИКА
Після зруйнування Чортомлицької Січі російськими військами полковника Яковлєва та козаками Гната Галаган між запорожцями та турецьким султаном Ахметом ІІІ було укладено pacta conventa. За умовами угоди при впадінні річки Кам’янки в Дніпро, вище сьогоднішнього м. Берислава (Кизикермена) запорожцями була заснована Кам’янська Січ. Топографія Січі підтверджувалася свідченням козацьких істориків ХVIII ст. С. Мишецьким, документальними джерелами із січового архіву, архіву Малоросійської колегії, дослідженнями археологічних експедицій Державного історико-культурного заповідника запорозького козацтва на о. Хортиця в 1971-1975 рр. та ін. Археологічні знахідки свідчать, що Кам’янська Січ проіснувала близько 8 років з однією тривалою перервою (1712-1728), коли Запорожці сиділи в шостій по числу – Олешківській Січі. Після трагедії на Чортомлицькій Січі новий кошовий спадкоємець героя Полтавської баталії Костя Гордієнка, енергійний і кмітливий Яків Богуш організував опір козаків Чортомлицької Січі, а потім очолив їх і заклав Кам’янську Січ
Shear flow effects on phase separation of entangled polymer blends
We introduce an entanglement model mixing rule for stress relaxation in a polymer blend to a modified Cahn-Hilliard equation of motion for concentration fluctuations in the presence of shear flow. Such an approach predicts both shear-induced mixing and demixing, depending on the relative relaxation times and plateau moduli of the two components
An Invariance Principle of G-Brownian Motion for the Law of the Iterated Logarithm under G-expectation
The classical law of the iterated logarithm (LIL for short)as fundamental
limit theorems in probability theory play an important role in the development
of probability theory and its applications. Strassen (1964) extended LIL to
large classes of functional random variables, it is well known as the
invariance principle for LIL which provide an extremely powerful tool in
probability and statistical inference. But recently many phenomena show that
the linearity of probability is a limit for applications, for example in
finance, statistics. As while a nonlinear expectation--- G-expectation has
attracted extensive attentions of mathematicians and economists, more and more
people began to study the nature of the G-expectation space. A natural question
is: Can the classical invariance principle for LIL be generalized under
G-expectation space? This paper gives a positive answer. We present the
invariance principle of G-Brownian motion for the law of the iterated logarithm
under G-expectation
Unfolding dynamics of proteins under applied force
Understanding the mechanisms of protein folding is a major challenge that is being addressed effectively by collaboration between researchers in the physical and life sciences. Recently, it has become possible to mechanically unfold proteins by pulling on their two termini using local force probes such as the atomic force microscope. Here, we present data from experiments in which synthetic protein polymers designed to mimic naturally occurring polyproteins have been mechanically unfolded. For many years protein folding dynamics have been studied using chemical denaturation, and we therefore firstly discuss our mechanical unfolding data in the context of such experiments and show that the two unfolding mechanisms are not the same, at least for the proteins studied here. We also report unexpected observations that indicate a history effect in the observed unfolding forces of polymeric proteins and explain this in terms of the changing number of domains remaining to unfold and the increasing compliance of the lengthening unstructured polypeptide chain produced each time a domain unfolds
Dumbbell transport and deflection in a spatially periodic potential
We present theoretical results on the deterministic and stochastic motion of
a dumbbell carried by a uniform flow through a three-dimensional spatially
periodic potential. Depending on parameters like the flow velocity, there are
two different kinds of movement: transport along a potential valley and
stair-like motion oblique to the potential trenches. The crossover between
these two regimes, as well as the deflection angle, depends on the size of the
dumbbell. Moreover, thermal fluctuations cause a resonance-like variation in
the deflection angle as a function of the dumbbell extension.Comment: 5 pages, 8 figure
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