623 research outputs found
Ep. #072 - Alexei Yurchak
No full textThis recording and transcript form part of a collection of podcasts conducted by the Cultures of Energy at Rice University. Cultures of Energy brings writers, artists and scholars together to talk, think and feel their way into the Anthropocene. We cover serious issues like climate change, species extinction and energy transition. But we also try to confront seemingly huge and insurmountable problems with insight, creativity and laughter.To help us sort through a week dominated by spiraling Russo-American political intrigue, we welcome (13:01) to the podcast Berkeley anthropologist, Alexei Yurchak, analyst extraordinaire of all things late Soviet and post Soviet, and author of the award-winning Everything was Forever Until It Was No More: The Last Soviet Generation (Princeton, 2005). We trace the connections between that project’s exploration of culture and politics at the end of state socialism and Alexei’s current research on the scientists who have been working to preserve Lenin’s body since 1924. We talk about the fascinating intersection of biopolitics and necropolitics involved in the effort to maintain Lenin’s body in a lifelike state for almost a century, how discursive hegemony of form in the late Soviet period also informed corporeal hegemony of form, the results of this science that you can find in your own pharmacy, and the network of political leaders’ bodies across the world that Soviet and now Russian scientists have worked to preserve. Alexei dispels the idea that cloning was ever on the table in this project; but explains that his interlocutors do believe that they can now keep Lenin’s body in a near-life state in perpetuity. We return from there to the contemporary political chaos and what Alexei makes of the Trump-Putin entanglement stories currently dominating the headlines. Alexei shares his concerns about the powerful return of Russophobia to the United States, about what popular characterizations of Russia get wrong, and about how anti-Russian sentiment may provide a convenient excuse to defer a serious examination of the root causes of Trumpism. Ready to take a break from the political hysteria? Then listen on
Complex plasmas: Interaction potentials and non-Hamiltonian dynamics
No full textThis thesis is a cumulative dissertation that consists of three papers.
The first paper addresses the issue of screening of a charged dust particle suspended in the plasma-wall transition layer of a plasma discharge. This problem is one of the fundamental issues in the physics of complex (dusty) plasmas, because the screening of charged dust particles determines the interaction forces between them and thus governs their dynamics. The kinetic model proposed in this paper considers a point charge embedded in a weakly-ionized plasma with ion drift. The latter is considered to be due to an external electric field and assumed to be mobility-limited. Here, "mobility-limited" means that the acceleration of ions in the external field is balanced by collisions of ions with neutrals and that this balance determines the drift velocity. The embedded point charge (i.e., a charged dust particle) perturbs the ion drift, and the resulting potential distribution around the dust particle is calculated. The results are proven to be in agreement with existing measurements performed in the plasma-wall transition layer of a rf plasma discharge. One of the important applications of this work is related to the possibility of tuning the pair interaction potential between dust particles by applying an external oscillating electric field. In particular, such a tuning allows studying electrorheological properties of strongly coupled systems on all relevant time scales. First experiments of this kind have already been performed onboard the International Space Station.
The second paper deals with the dust-lattice waves - oscillations of charged dust particles forming a crystalline structure in a plasma. The role of anisotropic screening of dust particles and variations of their charges is investigated. It is well known that the mentioned effects lead to non-Hamiltonian dynamics of dust particles and, as a result, can trigger an instability of the dust-lattice waves. This instability has been already observed in experiments. The new result is that the mutual influence of particles on their charges, not considered in the analysis of the dust-lattice waves before, is shown to be capable of making a significant contribution to this instability.
The third paper examines whether a similar instability can be observed in a cluster formed by two or three charged dust particles. It is found that an instability due to the non-Hamiltonian dynamics is only possible when the interparticle separation in the cluster is such that certain cluster eigenfrequencies are sufficiently close to each other.Настоящая диссертация является кумулятивной диссертацией и состоит из трех работ.
Первая работа посвящена экранированию заряженной пылевой частицы, левитируемой в приэлектродном слое плазменного разряда. Эта задача является одной из фундаментальных проблем физики пылевой плазмы, так как экранирование заряженных пылевых частиц определяет силы взаимодействия между ними и поэтому определяет их динамику. В статье предложена кинетическая модель, в которой рассматривается точечный заряд, помещенный в слабоионизированную плазму с ионным дрейфом. Предполагается, что ионный дрейф вызван внешним электрическим полем и соответствует мобильности ионов. Последнее означает, что подразумевается баланс между ускорением ионов во внешнем электрическом поле и столкновениями ионов с нейтралами, который и определяет скорость дрейфа. Внесенный точечный заряд (т.е., заряженная пылевая частица) возмущает дрейф ионов, и образующееся распределение потенциала вокруг пылевой частицы вычислено в настоящей работе. Результаты находятся в согласии с ранее опубликованными результатами измерений, выполненными в приэлектродном слое радиочастотного плазменного разряда. Одно из важных приложений этой работы связано с возможностью регулирования потенциала парного взаимодействия пылевых частиц посредством приложения внешнего осциллирующего электрического поля. В частности, такое регулирование позволяет изучать электрореологические свойства систем, в которых потенциальная энергия парного взаимодействия частиц превышает их кинетическую энергию. Первые эксперименты такого типа уже были проведены на борту Международной Космической Станции.
Предметом исследования второй работы являются так называемые пылекристаллические волны - колебания заряженных пылевых частиц, образующих кристаллическую структуру в плазме. Исследована роль как анизотропии экранирования пылевых частиц, так и вариаций их зарядов. Как известно, эти эффекты приводят к негамильтоновой динамике пылевых частиц и поэтому могут вызвать неустойчивость пылекристаллических волн, которая уже была обнаружена в экспериментах. Новый результат заключается в том, что взаимное влияние пылевых частиц на их заряды, которое ранее не учитывалось при анализе пылекристаллических волн, может обеспечить значительный вклад в эту неустойчивость.
В третьей работе исследовано, может ли подобная неустойчивость наблюдаться в кластере, состоящем из двух или трех пылевых частиц. Получено, что подобная неустойчивость из-за негамильтоновой динамики может возникнуть только тогда, когда расстояние между пылевыми частицами близко к резонансному значению, при котором определенные собственные частоты кластера совпадают.Diese Dissertation ist eine kumulative Dissertation und besteht aus drei Arbeiten.
Die erste Arbeit beschäftigt sich mit der Abschirmung des in einer Plasmarandschicht zur Schwebe gebrachten geladenen Staubteilchens. Dieses Problem ist von fundamentaler Bedeutung für die Physik der komplexen (staubigen) Plasmen, weil die Abschirmung die Form der Wechselwirkungen und somit die Dynamik der geladenen Staubteilchen bestimmt. In der Arbeit wird ein kinetisches Modell vorgeschlagen, in welchem ein Staubteilchen als eine Punktladung betrachtet wird, die sich in einem schwach ionisierten Plasma mit einer Ionendrift befindet. Es wird angenommen, dass die Ionendrift durch ein externes elektrisches Feld verursacht wird und dass diese Ionendrift der Mobilität der Ionen entspricht. Dies bedeutet, dass die Beschleunigung der Ionen im externen elektrischen Feld durch Ionen-Neutralteilchen-Stöße ausgeglichen wird und dass diese Kompensation die Geschwindigkeit der Ionendrift bestimmt. Die Punktladung (d.h. das Staubteilchen) stört diese Ionendrift, und in der vorliegenden Arbeit wird die resultierende Potentialverteilung des Staubteilchens im Plasma berechnet. Zudem wird festgestellt, dass die Resultate mit den früher in RF-Entladungen durchgeführten Experimenten konsistent sind. Die übergreifende Bedeutung dieser Untersuchung liegt in der Möglichkeit, damit durch ein externes elektrisches Wechselfeld das binäre Wechselwirkungspotential der Staubteilchen von außen zu steuern und somit z.B. elektrorheologische Eigenschaften von stark wechselwirkenden Systemen von Partikeln sichtbar zu machen und dynamisch auf allen relevanten Zeitskalen zu untersuchen. Erste Messungen dieser Art sind in Experimenten auf der Internationalen Raumstation bereits erfolgreich durchgeführt worden.
Die zweite Arbeit beschäftigt sich mit den sogenannten Staub-Gitter-Wellen (dust-lattice waves). Das sind Wellen, die durch Schwankungen der geladenen Staubteilchen, die eine Kristallstruktur im Plasma bilden, entstehen. In der vorliegenden Arbeit wird die Rolle sowohl der Anisotropie der Abschirmung der Staubteilchen als auch der Variation ihrer Ladungen untersucht. Wie bekannt führen diese Effekte zu nicht-Hamiltonischer Dynamik der Staubteilchen und können daher eine Instabilität der Staub-Gitter-Wellen auslösen. Solche Effekte sind in Experimenten bereits beobachtet worden. Das neue Ergebnis besteht darin, dass der gegenseitige Einfluss der Staubteilchen auf ihre Ladungen, ein Effekt, welcher bisher bei der Analyse der Staub-Gitter-Wellen noch nicht berücksichtigt wurde, einen wichtigen Beitrag zu dieser Instabilität leisten kann.
In der dritten Arbeit wird untersucht, ob eine ähnliche Instabilität in Partikelclustern, welche nur aus zwei oder drei Staubteilchen bestehen, beobachtet werden kann. Es wurde festgestellt, dass eine ähnliche Instabilität, die durch nicht-Hamiltonische Dynamik verursacht ist, nur dann möglich ist, wenn der Teilchenabstand so gewählt wird, dass bestimmte Eigenfrequenzen des Clusters gut miteinander übereinstimmen
Dust grains cannot grow to millimeter sizes in protostellar envelopes
No full textA big question in the field of star and planet formation is the time at which
substantial dust grain growth occurs. The observed properties of dust emission
across different wavelength ranges have been used as an indication that
millimeter-sized grains are already present in the envelopes of young
protostars. However, this interpretation is in tension with results from
coagulation simulations, which are not able to produce such large grains in
these conditions. In this work, we show analytically that the production of
millimeter-sized grains in protostellar envelopes is impossible under the
standard assumptions about the coagulation process. We discuss several
possibilities that may serve to explain the observed dust emission in the
absence of in-situ grain growth to millimeter sizes.Comment: Accepted to Ap
Production of atomic hydrogen by cosmic rays in dark clouds
No full textContext. Small amounts of atomic hydrogen, detected as absorption dips in the 21 cm line spectrum, are a well-known characteristic of dark clouds. The abundance of hydrogen atoms measured in the densest regions of molecular clouds can only be explained by the dissociation of H2 by cosmic rays. Aims. We wish to assess the role of Galactic cosmic rays in the formation of atomic hydrogen, for which we use recent developments in the characterisation of the low-energy spectra of cosmic rays and advances in the modelling of their propagation in molecular clouds. Methods. We modelled the attenuation of the interstellar cosmic rays that enter a cloud and computed the dissociation rate of molecular hydrogen that is due to collisions with cosmic-ray protons and electrons as well as fast hydrogen atoms. We compared our results with the available observations. Results. The cosmic-ray dissociation rate is entirely determined by secondary electrons produced in primary ionisation collisions. These secondary particles constitute the only source of atomic hydrogen at column densities above ~1021 cm-2. We also find that the dissociation rate decreases with column density, while the ratio between the dissociation and ionisation rates varies between about 0.6 and 0.7. From comparison with observations, we conclude that a relatively flat spectrum of interstellar cosmic-ray protons, such as suggested by the most recent Voyager 1 data, can only provide a lower bound for the observed atomic hydrogen fraction. An enhanced spectrum of low-energy protons is needed to explain most of the observations. Conclusions. Our findings show that a careful description of molecular hydrogen dissociation by cosmic rays can explain the abundance of atomic hydrogen in dark clouds. An accurate characterisation of this process at high densities is crucial for understanding the chemical evolution of star-forming regions
Penetration of Cosmic Rays into Dense Molecular Clouds: Role of Diffuse Envelopes
No full textTalk given by Alexei Ivle
The First Name Alexei: a Motif in The Brothers Karamazov
No full textРассматривается проблема обоснования гипотезы автобиографической мотивировки имени Алексея Карамазова на уровне поэтики романа «Братья Карамазовы». Доказывается, что память о младшем сыне Достоевского в значительной степени определяет топику и ряд значимых мотивов романа, одним из которых является само имя «Алексей».The article studies the problem of the hypothesis foundation of the autobiographic motivation for Alexei Karamazov's name with reference to the poetics of the novel The Brothers Karamazov. The author argues that Dostoyevsky's memories of his younger son determine the topic and a number of the novel's most significant motifs to a considerable extent, one of the motifs being the name Alexei proper
Alexei Miller, The Romanov Empire and Nationalism
No full textA new imperial history of the Russian Empire hardly breaks new ground — reprints of older publications show that this paradigm shift is well established by now. However, Alexei Miller’s anthology demonstrates that this approach can still pose stimulating questions and provide complex and unexpected answers. The book presents more than a welcomed English collection of Miller’s main publications: some of the contributions are new, some have undergone “significant changes,” as the author puts it..
Alexei Miller, The Romanov Empire and Nationalism
No full textA new imperial history of the Russian Empire hardly breaks new ground — reprints of older publications show that this paradigm shift is well established by now. However, Alexei Miller’s anthology demonstrates that this approach can still pose stimulating questions and provide complex and unexpected answers. The book presents more than a welcomed English collection of Miller’s main publications: some of the contributions are new, some have undergone “significant changes,” as the author puts it..
Shear-induced ordering in a liquid complex plasma
No full textA complex, or dusty plasma is a suspension of small solid particles in an ionized gas. Particles get charged by collecting electrons and ions from the ambient plasma and interact with each other via a screened Coulomb (Yukawa) pair potential. Complex plasmas are often strongly coupled and can exist in liquid and even crystallized forms.
In our experiment [1], polymer microspheres with a diameter of 9.19 μm were suspended in the plasma sheath above the lower electrode in a radio-frequency discharge in argon. The particle suspension self-organized in a highly ordered single-layer triangular lattice. Shear stress was applied to this plasma crystal by pushing a stripe of particles by the radiation pressure force of a rastered laser beam. We applied increasing levels of shear stress to the crystal. At low stress, the crystal deformed elastically. At higher stress, the following stages were observed: defect generation while in a solid state, onset of plastic flow, and fully developed shear flow.
We observed shear-induced reordering in a flowing liquid complex plasma. We made two related observations. First, a flowing liquid complex plasma is not completely isotropic. Rather, on top of an isotropic particle distribution appears a weak triangular order with Θ=0° (where Θ is the angle between the laser beam and the closely packed rows of particles) even in the cases when the original triangular lattice was oriented at 30°. Similar anisotropy in a liquid complex plasma was observed in [2], where the initial triangular order with Θ=0° was not completely destroyed in a shear melted state. Second, after the laser was switched off, the liquid complex plasma re-crystallized in a triangular lattice with Θ=0°, even though the lattice was oriented at Θ=30° before melting.
A flowing liquid complex plasmas, therefore, favors particle ordering where "closely packed lines" are oriented along the flow. The observed particle ordering is similar to the formation of particle strings aligned in the flow direction in sheared 2D colloidal dispersions [3] and simulated liquid of soft disks [4]. Here, we observed it for the first time in a sheared complex plasma.
[1] V. Nosenko, A. V. Ivlev, and G. E. Morfill, Phys. Rev. E 87, 043115 (2013).
[2] V. Nosenko, A. V. Ivlev, and G. E. Morfill, Phys. Rev. Lett. 108, 135005 (2012).
[3] E. J. Stancik, A. L. Hawkinson, J. Vermant, G. G. Fuller, J. Rheol. 48, 159 (2004).
[4] S. Butler and P. Harrowell, Phys. Rev. E 54, 457 (1996)
Particle Pairing In Complex Plasmas
No full textPairing of particles is a ubiquitous phenomenon in complex plasmas. The latter are suspensions of charged micron-size solid particles in a plasma, often in the (pre)sheath area above the lower electrode in a gas discharge [1]. Particle pairing was observed in various settings from isolated pairs and larger strings to pairs in 2D crystals and particle bilayers. An important role in the formation of particle pairs belongs to the plasma wakes that appear behind charged particles in the flow of ions. Fundamental questions are what determines the spatial extent of pairs and their stability. These questions recently received attention, but to the best of our knowledge no systematic study was done.
In this work, we systematically study the dependence of particle pair size on experimental parameters. We used an experimental setup based on a modified Gaseous Electronics Conference (GEC) radio-frequency (rf) reference cell [2]. Plasma was sustained by a capacitively coupled rf discharge in argon at the pressure of 2 Pa. Melamine-formaldehyde (MF) microspheres with a diameter of 9.19±0.09 μm were suspended in the (pre)sheath area above the lower rf electrode. The particle suspension was imaged from the top and side with two video cameras.
A specially designed "pair state" of complex plasma was prepared where particles formed multiple pairs that were vertically oriented, had a well-defined size, and levitated at the same height but were weakly coupled with each other and did not form any regular structure. As the discharge voltage was decreased, the pairs shifted downward and extended vertically. The vertical size of pairs was measured as a function of experimental parameters. We offer an interpretation of our observations based on a recent theory [3] that takes plasma non-uniformity into account.
[1] A. Ivlev, H. Löwen, G. Morfill, C. P. Royall, Complex Plasmas and Colloidal Dispersions: Particle-resolved Studies of Classical Liquids and Solids, Series in Soft Condensed Matter Vol. 5 (World Scientific, Singapore, 2012).
[2] V. Nosenko, A. V. Ivlev, and G. E. Morfill, Phys. Rev. E 87, 043115 (2013).
[3] R. Kompaneets, A. V. Ivlev, V. Nosenko, and G. E. Morfill, Phys. Rev. E, accepted (2014)
- …
