What is statistical mechanics?

Statistical mechanics explains the simple behavior of complex systems. It works by studying not a particular instance, but the typical behavior of a large collection (or ensemble) of systems, which is far easier to calculate. Entropy, free energies, order parameters, phases and phase transitions emerge as collective behaviors that are not manifest in the complex microscopic laws. This text will develop the statistical mechanical machinery needed to generate the new laws governing these emergent behaviors. Exercises in this chapter discuss emergence, Stirling’s formula, random matrix theory, small world networks, an NP complete problem, active matter, and topics in statistics.

An optic ray theory for durotactic axon guidance

During the development of the nervous system, neurons extend bundles of axons that grow and meet other neurons to form the neuronal network. Robust guidance mechanisms are needed for these bundles to migrate and reach their functional target. Directional information depends on external cues such as chemical or mechanical gradients. Unlike chemotaxis that has been extensively studied, the role and mechanism of durotaxis, the directed response to variations in substrate rigidity, remain unclear. We model bundle migration and guidance by rigidity gradients by using the theory of morphoelastic rods. We show that at a rigidity interface, the motion of axon bundles follows a simple behavior analogous to optic ray theory and obeys Snell’s law for refraction and reflection. We use this powerful analogy to demonstrate that axons can be guided by the equivalent of optical lenses and fibers created by regions of different stiffnesses.

Photo-Mechanical Response Dynamics of Liquid Crystal Elastomer Linear Actuators

With continuous miniaturization of many technologies, robotics seems to be lagging behind. While the semiconductor technologies operate confidently at the nanometer scale and micro-mechanics of simple structures (MEMS) in micrometers, autonomous devices are struggling to break the centimeter barrier and have hardly colonized smaller scales. One way towards miniaturization of robots involves remotely powered, light-driven soft mechanisms based on photo-responsive materials, such as liquid crystal elastomers (LCEs). While several simple devices have been demonstrated with contracting, bending, twisting, or other, more complex LCE actuators, only their simple behavior in response to light has been studied. Here we characterize the photo-mechanical response of a linear light-driven LCE actuator by measuring its response to laser beams with varying power, pulse duration, pulse energy, and the energy spatial distribution. Light absorption decrease in the actuator over time is also measured. These results are at the foundation of further development of soft, light-driven miniature mechanisms and micro-robots.

How efficient are the lockdown measures taken for mitigating the Covid-19 epidemic?

Various lockdown measures have been taken in different countries to mitigate the Covid-19 pandemic. But, for citizens, it is not always simple to understand how these measures have been taken. Should they have been more (or less) restrictive? Should the lockdown period have been longer (or shorter)? What would have been the benefits of starting to confine the population earlier? To provide some elements of response to these questions, we propose a simple behavior model for the government decision-making operation. Although simple and obviously improvable, the proposed model has the merit to implement in a pragmatic and insightful way the tradeoff between health and macroeconomic aspects. For a given tradeoff between the assumed cost functions for the economic and health impacts, it is then possible to determine the best lockdown starting date, the best lockdown duration, and the optimal severity levels during and after lockdown. The numerical analysis is based on a standard SEIR model and performed for the case of France but the adopted approach can be applied to any country. Our analysis, based on the proposed model, shows that for France it would have been possible to have just a quarter of the actual number of people infected (over [March 1, August 31]), while simultaneously having a Gross Domestic Product loss about 30% smaller than the one expected with the current policy

Levels of Intelligence

Intelligence is the ability to find solutions to complex problems a life faces in a complex and uncertain environment. This cannot be captured by a standardized numerical score, such as IQ, that focuses on a narrow range of cognitive capabilities, such as working memory or verbal fluency. Intelligence also cannot be separated from the most essential property of all life forms, which is self-replication. This chapter briefly reviews the evolutionary history and diversity of intelligence from single-cell organisms to humans. The chapter includes a definition of intelligence and a discussion of how the nervous system works, the simple behavior of reflexes and the limitations of reflexes, connectome (the comprehensive map of all the connections in an animal’s nervous system), the multiple controllers for muscles, and the social nature of many behaviors. The chapter also includes a case study on eye movements.

Simple catchments and where to find them: The storage discharge relationship as a proxy for catchment complexity

<p>Hydrology and especially hydrological models often treat catchments as if they were leaky buckets. But, do we find such catchments in the real world or is this just a convenient simplification? Moreover, if we find them, what attributes allow these catchments to show such a simple behavior? To study this, we look at time series of 27 years for 90 catchments in Hesse, Germany, which includes droughts and years of abundant precipitation. In addition, the state Hesse provides a wide range of catchment attributes like geology, soils and land use, while still having a relatively similar climate. Using discharge, evapotranspiration and precipitation, we calculate the cumulative storage change for all years separately and use it as a proxy for the storage. We group the 90 catchments by the complexity of their storage-discharge relationship, which we define as how good the relationship can be modelled by an exponential function. We find that climate and physical attributes of the catchments seem to have similar influence on the overall complexity of the storage-discharge relationship. However, we could also identify catchments that depict consistent behavior, mostly independent of climate. Those catchments either behave always complex or always simple in all the years considered. They differ in their permeability, conductivity, geology, soil and to a lesser extent their shape. We show that bucket like catchments exist in the real world and that they can be found by looking for oval catchments with good permeability in regions of igneous geology and clay silt soil texture.</p>

Experimental evaluation of eccentric rotational channel-type damping system for vibration control of building structures

A theoretical and experimental investigation of an eccentric rotational channel-type damping system is presented. The proposed damping system can incorporate any type of existing passive dampers and provide a wider field of view to residents compared with existing damping systems. Furthermore, the efficiency of the proposed damping system can be magnified by modifying the geometry of the channel-type secondary system. Cyclic loading and free vibration tests of a full-scale test model with steel dampers were conducted to investigate the validity of the suggested simple behavior prediction model and the vibration characteristics of the proposed damping system. The experimental results were in good agreement with the numerical analysis. The results of numerical prediction studies on a single degree of freedom system with the proposed damping system also showed the effect of the eccentric rotational channel-type damping system on seismic response reduction.

Planckian dissipation, minimal viscosity and the transport in cuprate strange metals

Could it be that the matter formed from the electrons in high Tc superconductors is of a radically new kind that may be called "many body entangled compressible quantum matter"? Much of this text is intended as an easy to read tutorial, explaining recent theoretical advances that have been unfolding at the cross roads of condensed matter- and string theory, black hole physics as well as quantum information theory. These developments suggest that the physics of such matter may be governed by surprisingly simple principles. My real objective is to present an experimental strategy to test critically whether these principles are actually at work, revolving around the famous linear resistivity characterizing the strange metal phase. The theory suggests a very simple explanation of this "unreasonably simple" behavior that is actually directly linked to remarkable results from the study of the quark gluon plasma formed at the heavy ion colliders: the "fast hydrodynamization" and the "minimal viscosity". This leads to high quality predictions for experiment: the momentum relaxation rate governing the resistivity relates directly to the electronic entropy, while at low temperatures the electron fluid should become unviscous to a degree that turbulent flows can develop even on the nanometre scale.

FAKTOR YANG MEMPENGARUHI KONSUMSI MASYAAKAT MISKIN DALAM PERSPEKTIF ISLAM

Factors that influence the consumption pattern of the poor in Islamic perspective have been analyzed in depth in this study. Inventory variables refer to the concept; Al-Ghazali which consists of aql, qalb and nafs. These three variables & nbsp; asymmetrically affect the tendency of consumption patterns. & nbsp; This study uses an explanatory survey method with data collection techniques through questionnaires and interviews. The population of 68 people who are recipients of zakat distributed by the Zakat Agency Bandung City. The data that has been collected is then analyzed by multiple regression. The results of the study show that consumption patterns & nbsp; poor people in Indonesia (Bandung City, West Java) are influenced by Aql, Qalb and Nafs. These three factors significantly and positively affect consumption patterns of the poor in the city of Bandung. This finding implies that the consumption of society should be Simple behavior. In accordance with Islamic principles, always instill within that the treasure given by God is merely a deposit, and is not easily influenced by fashion Abstrak Faktor-faktor yang mempengaruhi pola konsumsi masyarakat miskin dalam perpektif islam telah dianalisis secara mendalam dalam kajian ini. Variabel yang diinventarisir mengacu pada konsep Al-Ghazali yang terdiri dari aql, qalb dan nafs. Ketiga Variabel tersebut secara asimetris mempengaruhi kecenderungan pola konsumsi. Kajian ini menggunakan metode survey eksplanatory dengan teknik pengumpulan data melalui kuesioner dan wawancara. Populasi sebanyak 68 orang yang merupakan para penerima zakat yang disalurkan oleh Badan Amil Zakat Kota Bandung. Data yang telah dikumpulkan selanjutnya dianalisis dengan regeresi berganda. Hasil kajian menunjukkan bahwa pola konsumsi masyarakat miskin di Indonesia (Kota Bandung Jawa Barat) dipengaruhi oleh Aql, Qalb dan Nafs. Ketiga faktor tersebut secara signifikan dan berpengaruh positif terhadap pola konsumsi masyarakat miskin d Kota Bandung.Temuan ini mmberikan implikasi bahwa dalam berkonsumsi masyarakat hendaknya Berperilaku sederhana yang sesuai dengan prinsip islam, selalu menanamkan dalam diri bahwa sesungguhnya harta yang diberikan oleh Allah hanyalah titipan semata, dan tidak mudah terpengaruh oleh mode