Equation of State of Wet Granular Matter

A theory is derived for the nonequilibrium probability currents of the capillary interaction which determines the pair correlation function near contact. This yields an analytic expression for the equation of state, P = P(N/V,T), of wet granular matter for D=2 dimensions, valid in the complete density range from gas to jamming. Driven wet granular matter exhibits a van-der-Waals-like unstable branch at granular temperatures T<T_c corresponding to a first order segregation transition of clusters. For the realistic rupture length of the liquid bridge, s_crit=0.07 d, the critical point is located at T_c = 0.274 E_cb. While the critical temperature weakly depends on the rupture length, the critical density phi_c is shown to scale with s_crit according to s_crit = 4d (sqrt(phi_J / phi_c) -1). The segregation transition is closely related to the precipitation of granular droplets reported for the free cooling of one-dimensional wet granular matter [Phys. Rev. Lett. 97, 078001 (2006)], and extends the effect to higher dimensional systems. Since the limiting case of sticky bonds, E_cb >> T, is of relevance for aggregation in general, simulations have been performed which show very good agreement with the theoretically predicted coordination K of capillary bonds as a function of the bond length s_crit. This result implies that particles that stick at the surface, s_crit=0, form isostatic clusters.Comment: 29 pages, 20 figure

Chaoticity of the Wet Granular Gas

In this work we derive an analytic expression for the Kolmogorov-Sinai entropy of dilute wet granular matter, valid for any spatial dimension. The grains are modelled as hard spheres and the influence of the wetting liquid is described according to the Capillary Model, in which dissipation is due to the hysteretic cohesion force of capillary bridges. The Kolmogorov-Sinai entropy is expanded in a series with respect to density. We find a rapid increase of the leading term when liquid is added. This demonstrates the sensitivity of the granular dynamics to humidity, and shows that the liquid significantly increases the chaoticity of the granular gas.Comment: 13 pages, 10 figures, Physical Review

What you get is what you need? The role of venture capitalists in managing growth of new ventures

The resource-based view is suggested as a useful concept to shed light on the particular challenges of high potential companies on their way to building a thriving and growing company. In order to be able to apply the theoretical constructs of the resource-based view in the present context, a categorization of resources is elaborated that fits particularly well to high potential companies. Existing literature provides evidence that these companies in general only dispose of a small resource base and that they are characterized by strong resource needs in all relevant resource categories. The role of venture capitalists is assumed to provide high potential companies with financial and non-financial resources that help to create core and non-core competencies. Ultimately, this bundle of core and non-core competencies would allow high potential companies to achieve a sustained competitive advantage. The empirical results of this paper are based on insights from three in-depth case studies on German start-ups, each representing a different investor-investee dyad. It comprises investees from different industries such as software, biotech, and energy as well as investors with an established track record, first fund investors, and semi-government-dependent investors. The cases show that venture capitalists provide a number of resources to their portfolio companies that allow building a competitive advantage. The role of the venture capitalists is thus to help high potential companies to complement existing resources and competences in order to develop their full economic potential. However, there is great variation between the resource provisions of the analyzed venture capital firms. --Entrepreneurship,Venture Capital,Resource-based View

Relativistic Fluctuation Theorems: Theory and explicit examples

To reveal how nonequilibrium physics and relativity theory intertwine, this articles studies relativistic Brownian motion under cosmic expansion. Two fluctuation theorems for the entropy ds, which is locally produced in this extreme nonequilibrium situation, are presented and proven. The first, =1, is a generalization of the second law of thermodynamics, that remains valid at relativistic particle energies and under high cosmic expansion rates. From this relation follows, that the probability to observe a local reduction of entropy is exponentially small even if the universe was to recollapse. For the special case of the Einstein-de Sitter universe an additional relation, =1, is derived which holds simultaneously with the first relation and where dh is proportional to the Hubble constant. Furthermore, the fluctuation theorems are shown to provide a physical criterion to resolve the known discretization dilemma arising in special-relativistic Brownian motion. Explicit examples and a general method for the computation of non-Gaussian entropy fluctuations are provided.Comment: 27 pages, 6 figures, Comptes rendus - Physiqu

A study of the inter-annual variation of the onset of the North American Monsoon

The purpose of this study was to identify the climatological variability in onset dates for the North American Monsoon in order to gain a better understanding of the North American Monsoon. The NARR reanalysis data set from 1979-2010 was used to supply daily rainfall totals in northwestern Mexico, one of the three major areas impacted yearly by the monsoon (Barlow 1998). From this data, monsoon rainfall onset was defined as when daily precipitation surpassed 2mm (Barlow 1998). This study strove to prove that the average monsoon onset was on or about the 1st of July each year over the 30 year period, using the aforementioned NARR data and the established monsoon onset parameters. At the same time, monsoon season total rainfall data was collected, to use for later comparison. Over the course of the study, a large variability was found in the monsoon onset date, and thus, the study continued by attempting to find a atmospheric trigger that would indicate when monsoon onset was going to occur each year. In order to compare the monsoon onset to various tele-connection patterns, the period of monsoon variability was broken up into five different periods, with the middle period representing 50% of the monsoon onset dates—the most common onset dates—and the periods on either side representing significant deviations from the mean. Each of the five periods of monsoon onset were then compared to various different indices including: variation in sea surface temperatures, the El Niño-Southern Oscillation (ENSO), the Pacific-North American Tele-connection Pattern (PNA), and the Pacific Decadal Oscillation (PDO). These indices were chosen because they had been identified in the literature as possibly contributing to the climatology of the North American Monsoon (Gao 2007, Adams 1997). Monsoon onset was also compared to Iowa summer rainfall totals, for the purpose of comparison with a mid-latitude system. The goal of these comparisons was to determine if a particular phase of a teleconnection pattern or spike in sea surface temperatures (SST) or mid-latitude rainfall could be used to indicate when the monsoon onset would take place in Northwestern Mexico. Following these lines of questioning, the study was able to determine that the average onset date of the North American Monsoon is 25 June, with a 40 day window of variability over the 30 years which were studied. Breaking the monsoon onset window into smaller periods allowed for a comparison between monsoon onset with monsoon total rainfall, Iowa season rainfall, sea surface temperatures, and other tele-connection patterns. The most significant correlation found was between early monsoon onset and above average sea surface temperatures in the Pacific Ocean, while other correlations were found regarding above average monsoon total season rainfall and the Pacific Decadal Oscillation

MIF coordinates the cell cycle with DNA damage checkpoints. Lessons from knockout mouse models

Macrophage migration inhibitory factor (MIF) is a ubiquitously expressed pro-inflammatory mediator that has also been implicated in the process of oncogenic transformation and tumor progression. We used a genetic approach to show that deletion of the MIF gene in mice has several major consequences for the proliferative and transforming properties of cells. MIF-deficient cells exhibit increased resistance to oncogenic transformation. The transformation defects associated with MIF deficiency can be overcome through concomitant inactivation of the p53 and Rb/E2F tumor suppressor pathways. We have produced compelling evidence that the effects of MIF on cell survival and tumorigenesis are mediated through overlapping pathways, wherein MIF and p53 functionally antagonize each other in the cell. However, the involvement of MIF in p53 function is secondary to p53-independent mechanisms controlling protein stability, DNA damage checkpoints, and the integrity of the genome. Given the broad spectrum of cell types that normally express MIF and its elevated levels at sites of chronic inflammation, this pathway may be generic for many early stage tumors

Cooling and aggregation in wet granulates

Wet granular materials are characterized by a defined bond energy in their particle interaction such that breaking a bond implies an irreversible loss of a fixed amount of energy. Associated with the bond energy is a nonequilibrium transition, setting in as the granular temperature falls below the bond energy. The subsequent aggregation of particles into clusters is shown to be a self-similar growth process with a cluster size distribution that obeys scaling. In the early phase of aggregation the clusters are fractals with D_f=2, for later times we observe gelation. We use simple scaling arguments to derive the temperature decay in the early and late stages of cooling and verify our results with event-driven simulations.Comment: 4 pages, 6 figures, suggestions of the referees implemented, EPAPS supplementary material added: http://netserver.aip.org/cgi-bin/epaps?ID=E-PRLTAO-102-00391

Dilute Wet Granulates: Nonequilibrium Dynamics and Structure Formation

We investigate a gas of wet granular particles, covered by a thin liquid film. The dynamic evolution is governed by two-particle interactions, which are mainly due to interfacial forces in contrast to dry granular gases. When two wet grains collide, a capillary bridge is formed and stays intact up to a certain distance of withdrawal when the bridge ruptures, dissipating a fixed amount of energy. A freely cooling system is shown to undergo a nonequillibrium dynamic phase transition from a state with mainly single particles and fast cooling to a state with growing aggregates, such that bridge rupture becomes a rare event and cooling is slow. In the early stage of cluster growth, aggregation is a self-similar process with a fractal dimension of the aggregates approximately equal to D_f ~ 2. At later times, a percolating cluster is observed which ultimately absorbs all the particles. The final cluster is compact on large length scales, but fractal with D_f ~ 2 on small length scales.Comment: 14 pages, 20 figure