Signatures for Black Hole production from hadronic observables at the Large Hadron Collider

The concept of Large Extra Dimensions (LED) provides a way of solving the Hierarchy Problem which concerns the weakness of gravity compared with the strong and electro-weak forces. A consequence of LED is that miniature Black Holes (mini-BHs) may be produced at the Large Hadron Collider in p+p collisions. The present work uses the CHARYBDIS mini-BH generator code to simulate the hadronic signal which might be expected in a mid-rapidity particle tracking detector from the decay of these exotic objects if indeed they are produced. An estimate is also given for Pb+Pb collisions.Comment: 11 pages, 9 figures, ISHIP 2006 conference proceedin

The Structure and Activation of Soluble Guanylate Cyclase

The biochemical signaling pathways that involve gaseous primary signaling molecules have only been characterized in the last three decades, due to the small diversity of diatomic gases and the lack of other known physiological functions of these gases (apart from O2 as the terminal electron acceptor in oxidative phosphorylation). In general, certain events must take place for any process to be considered biochemical signaling: the primary signaling molecule must be synthesized and excreted from the generator cell or be present or absent in the environment, that signaling molecule must come in contact with its specific receptor molecule within the receiving cell, and the receptor molecule must transduce the primary singling molecule into a secondary signal which activates downstream signaling pathways. Only a pathway that is comprised of signal generation, the primary signal, and signal reception constitutes a complete biochemical signaling pathway. In spite of the relatively recent discovery, gaseous signaling molecules control critical signaling pathways in many aspects of organismal physiology.In the 1980s, two different lines of research serendipitously came together to describe the first gaseous biochemical signaling pathway. The first was pharmacologists’ observation that vasculature that had the endothelium removed would constrict, and thus there must be an Endothelium Derived Relaxation Factor (EDRF) that maintained appropriate vasculature tone. Curiously, EDRF had the exact same chemical properties as nitric oxide (NO), however there was no known biotic source of this toxic gas. The second line of research centered on the observation that excreted nitrates spiked in concentration when sickness was incurred, even when nitrate intake remained the same. This led to the discovery that macrophages synthesize the cytotoxic agent NO to attack invading pathogens, and thus a biotic source of NO had been discovered. The EDRF and NO were shown to be one and the same, and this coupled with the fact that soluble guanylate cyclase had been known to be stimulated by NO since the 1970s provided the receptor of the first gaseous biochemical signaling pathway.The enzyme responsible for the generation of NO is nitric oxide synthase (NOS) (EC 1.14.13.39). NOS catalyzes the 5-electron oxidation of arginine to citrulline and NO. There are three different isoforms of NOS in Homo sapiens, inducible NOS (iNOS), endothelial NOS (eNOS), and neuronal (nNOS). Nitric oxide synthases are activated by calcium-bound calmodulin (Ca2+-CaM). iNOS has a high affinity for Ca2+-CaM, and thus is regulated at the transcriptional level in macrophages where it synthesizes NO at sites of infection or inflammation. eNOS and nNOS have lower affinity for Ca2+-CaM and are constitutively expressed, which allows calcium gradients in neurons and endothelial cells to control the activation of these isoforms. For example, when endothelial cells hyperpolarize due to high blood pressure, intracellular concentrations of Ca2+ increase up to ten-fold which in turn increases Ca2+-CaM concentration and thus activates eNOS.Activated eNOS generates NO at nanomolar concentrations, which diffuses to nearby smooth muscle cells that express the mammalian NO receptor, soluble guanylate cyclase (sGC) (EC 4.6.1.2). sGC is a heterodimeric hemeoprotein which can sense NO at nanomolar concentrations. When NO binds to sGC, the enzyme increases its catalytic activity of cyclizing 5′-guanosine triphosphate (GTP) to 3′,5′-cyclic guanosine monophosphate (cGMP). The molecular mechanisms by which NO activates sGC are not completely understood. In particular, it is clear from experiments both in vitro and in cells that one equivalent of NO does not activate sGC to its maximal activity but only to a low activity state. Excess NO must be present in order to completely stimulate the enzyme. If that excess NO is removed either with a buffer exchange or a chemical trap, the enzyme returns to a low activity state. The increase in cellular concentration of cGMP activates a variety of downstream signaling proteins, including cGMP-dependent protein kinases, cGMP-regulated ion channels, and phosphodiesterases that mediate the downstream cell signaling cascade. The resultant phenotype of these cellular signaling molecules is the relaxation of the smooth muscle cells, the dilation of the vasculature, and the decrease of overall blood pressure. Thus, any malfunctions of this pathway can result in too high of blood pressure and increased risk of cardiovascular diseases.The NOS-NO-sGC-cGMP signaling pathway has been the target for stimulating therapeutics to treat forms of high blood pressure. A screen of small molecules that induce platelet aggregation found that the chemically synthesized benzylindazole YC-1 was able to stimulate sGC in a heme-dependent manner. Significant efforts in medicinal chemistry in the following two decades yielded riociguat, the first FDA-approved sGC stimulator that is used to treat certain forms of pulmonary hypertension. However, the specific binding site of YC-1 derived compounds on sGC and the reason for the specificity of these types of molecules against the soluble form of guanylate cyclases has not been elucidated. Additionally, atypical soluble guanylate cyclases have been described that sense O2 instead of NO. Thus, the possibility exists for gases other than NO and O2 to function as signaling molecules in eukaryotic organisms. These outstanding questions will be answered in the following thesis entitled: The Structure and Activation of Soluble Guanylate Cyclase

Mini black holes at the LHC : discovery through di-jet suppression, mono-jet emission and a supersonic boom in the quark-gluon plasma in ALICE, ATLAS and CMS

We examine experimental signatures of TeV-mass black hole formation in heavy ion collisions at the LHC. We find that the black hole production results in a complete disappearance of all very high p_T (> 500 GeV) back-to-back correlated di-jets of total mass M > M_f ~ 1 TeV. We show that the subsequent Hawking-decay produces multiple hard mono-jets and discuss their detection. We study the possibility of cold black hole remnant (BHR) formation of mass ~ M_f and the experimental distinguishability of scenarios with BHRs and those with complete black hole decay. Finally we point out that a Heckler-Kapusta-Hawking plasma may form from the emitted mono-jets. In this context we present new simulation data of Mach shocks and of the evolution of initial conditions until the freeze-out

Research Commentary: Setting a Definition, Context, and Theory-Based Research Agenda for the Gamification of Non-Gaming Applications

As a nascent area of study, gamification has attracted the interest of researchers in several fields, but such researchers have scarcely focused on creating a theoretical foundation for gamification research. Gamification involves using game-like features in non-game contexts to motivate users and improve performance outcomes. As a boundary-spanning subject by nature, gamification has drawn the interest of scholars from diverse communities, such as information systems, education, marketing, computer science, and business administration. To establish a theoretical foundation, we need to clearly define and explain gamification in comparison with similar concepts and areas of research. Likewise, we need to define the scope of the domain and develop a research agenda that explicitly considers theory’s important role. In this review paper, we set forth the pre-theoretical structures necessary for theory building in this area. Accordingly, we engaged an interdisciplinary group of discussants to evaluate and select the most relevant theories for gamification. Moreover, we developed exemplary research questions to help create a research agenda for gamification. We conclude that using a multi-theoretical perspective in creating a research agenda should help and encourage IS researchers to take a lead role in this promising and emerging area

Breaking Free from the Limitations of Classical Test Theory: Developing and Measuring Information Systems Scales Using Item Response Theory

Information systems (IS) research frequently uses survey data to measure the interplay between technological systems and human beings. Researchers have developed sophisticated procedures to build and validate multi-item scales that measure latent constructs. The vast majority of IS studies uses classical test theory (CTT), but this approach suffers from three major theoretical shortcomings: (1) it assumes a linear relationship between the latent variable and observed scores, which rarely represents the empirical reality of behavioral constructs; (2) the true score can either not be estimated directly or only by making assumptions that are difficult to be met; and (3) parameters such as reliability, discrimination, location, or factor loadings depend on the sample being used. To address these issues, we present item response theory (IRT) as a collection of viable alternatives for measuring continuous latent variables by means of categorical indicators (i.e., measurement variables). IRT offers several advantages: (1) it assumes nonlinear relationships; (2) it allows more appropriate estimation of the true score; (3) it can estimate item parameters independently of the sample being used; (4) it allows the researcher to select items that are in accordance with a desired model; and (5) it applies and generalizes concepts such as reliability and internal consistency, and thus allows researchers to derive more information about the measurement process. We use a CTT approach as well as Rasch models (a special class of IRT models) to demonstrate how a scale for measuring hedonic aspects of websites is developed under both approaches. The results illustrate how IRT can be successfully applied in IS research and provide better scale results than CTT. We conclude by explaining the most appropriate circumstances for applying IRT, as well as the limitations of IRT

Allosteric activation of the nitric oxide receptor soluble guanylate cyclase mapped by cryo-electron microscopy.

Soluble guanylate cyclase (sGC) is the primary receptor for nitric oxide (NO) in mammalian nitric oxide signaling. We determined structures of full-length Manduca sexta sGC in both inactive and active states using cryo-electron microscopy. NO and the sGC-specific stimulator YC-1 induce a 71° rotation of the heme-binding β H-NOX and PAS domains. Repositioning of the β H-NOX domain leads to a straightening of the coiled-coil domains, which, in turn, use the motion to move the catalytic domains into an active conformation. YC-1 binds directly between the β H-NOX domain and the two CC domains. The structural elongation of the particle observed in cryo-EM was corroborated in solution using small angle X-ray scattering (SAXS). These structures delineate the endpoints of the allosteric transition responsible for the major cyclic GMP-dependent physiological effects of NO

Braid Entropy of Two-Dimensional Turbulence

The evolving shape of material fluid lines in a flow underlies the quantitative prediction of the dissipation and material transport in many industrial and natural processes. However, collecting quantitative data on this dynamics remains an experimental challenge in particular in turbulent flows. Indeed the deformation of a fluid line, induced by its successive stretching and folding, can be difficult to determine because such description ultimately relies on often inaccessible multi-particle information. Here we report laboratory measurements in two-dimensional turbulence that offer an alternative topological viewpoint on this issue. This approach characterizes the dynamics of a braid of Lagrangian trajectories through a global measure of their entanglement. The topological length of material fluid lines can be derived from these braids. This length is found to grow exponentially with time, giving access to the braid topological entropy . The entropy increases as the square root of the turbulent kinetic energy and is directly related to the single-particle dispersion coefficient. At long times, the probability distribution of is positively skewed and shows strong exponential tails. Our results suggest that may serve as a measure of the irreversibility of turbulence based on minimal principles and sparse Lagrangian data