Symmetric Vacua in Heterotic M-Theory

Symmetric vacua of heterotic M-theory, characterized by vanishing cohomology classes of individual sources in the three-form Bianchi identity, are analyzed on smooth Calabi-Yau three-folds. We show that such vacua do not exist for elliptically fibered Calabi-Yau spaces. However, explicit examples are found for Calabi-Yau three-folds arising as intersections in both unweighted and weighted projective space. We show that such symmetric vacua can be combined with attractive phenomenological features such as three generations of quarks and leptons. Properties of the low energy effective actions associated with symmetric vacua are discussed. In particular, the gauge kinetic functions receive no perturbative threshold corrections, there are no corrections to the matter field Kahler metric and the associated five-dimensional effective theory admits flat space as its vacuum.Comment: 22 pages, Late

Recovery of corals a decade after a bleaching event in Dubai, United Arab Emirates

Elevated sea surface temperatures in the late 1990s were associated with widespread coral mortality in the Arabian Gulf, particularly in Acropora dominated areas. This study investigates the composition, condition, and recruitment patterns of coral communities in Saih Al-Shaib, Dubai, United Arab Emirates, a decade after mass bleaching. Five statistically distinct communities were identified by cluster analysis, with grouping optimized from 17 significant indicator species. Overall, 25 species of scleractinian coral were observed, representing 35 ± 1.6% coral cover. Densities of recruits were low (0.8 ± 0.2 m-2), and composition generally reflected that of the surrounding adult community. Ten years after mass mortality, Acropora dominated assemblages were observed in three of the six sites examined and coral cover (41.9 ± 2.5%) was double post-bleaching cover. One shallow near-shore site appears to have had recovery of Acropora reset by a further bleaching event in 2002. However, the prevalence of young Acropora colonies here indicates that recovery may recur in several years. One area formerly dominated by Acropora is now dominated by faviids and poritids, with adult and juvenile composition suggesting this dominance shift is likely to persist. Porites lutea and Porites harrisoni dominated communities were negligibly impacted by the bleaching events, and the limited change in coral cover and composition in intervening years likely results from slow growth and low recruitment. Despite strong recovery of several dominant Acropora species, five formerly common species from this area were not observed suggesting local extinction. Dubai coral communities exhibit both resistance and resilience to elevated sea temperatures. The conservation of these patch reefs is warranted given the predicted increase in bleaching events, and the role that these communities may play in regional recovery. © 2008 Springer-Verlag

Quantum hierarchic models for information processing

Both classical and quantum computations operate with the registers of bits. At nanometer scale the quantum fluctuations at the position of a given bit, say, a quantum dot, not only lead to the decoherence of quantum state of this bit, but also affect the quantum states of the neighboring bits, and therefore affect the state of the whole register. That is why the requirement of reliable separate access to each bit poses the limit on miniaturization, i.e, constrains the memory capacity and the speed of computation. In the present paper we suggest an algorithmic way to tackle the problem of constructing reliable and compact registers of quantum bits. We suggest to access the states of quantum register hierarchically, descending from the state of the whole register to the states of its parts. Our method is similar to quantum wavelet transform, and can be applied to information compression, quantum memory, quantum computations.Comment: 14 pages, LaTeX, 1 eps figur

Entangled and disentangled evolution for a single atom in a driven cavity

For an atom in an externally driven cavity, we show that special initial states lead to near-disentangled atom-field evolution, and superpositions of these can lead to near maximally-entangled states. Somewhat counterintutively, we find that (moderate) spontaneous emission in this system actually leads to a transient increase in entanglement beyond the steady-state value. We also show that a particular field correlation function could be used, in an experimental setting, to track the time evolution of this entanglement

Are artificial reefs surrogates of natural habitats for corals and fish in Dubai, United Arab Emirates?

Artificial reefs are often promoted as mitigating human impacts in coastal ecosystems and enhancing fisheries; however, evidence supporting their benefits is equivocal. Such structures must be compared with natural reefs in order to assess their performance, but past comparisons typically examined artificial structures that were too small, or were immature, relative to the natural reefs. We compared coral and fish communities on two large (\u3e400,000 m3) and mature (\u3e25 year) artificial reefs with six natural coral patches. Coral cover was higher on artificial reefs (50%) than in natural habitats (31%), but natural coral patches contained higher species richness (29 vs. 20) and coral diversity (H′ = 2.3 vs. 1.8). Multivariate analyses indicated strong differences between coral communities in natural and artificial habitats. Fish communities were sampled seasonally for 1 year. Multivariate fish communities differed significantly among habitat types in the summer and fall, but converged in the winter and spring. Univariate analysis indicated that species richness and abundance were stable throughout the year on natural coral patches but increased significantly in the summer on artificial reefs compared with the winter and spring, explaining the multivariate changes in community structure. The increased summer abundance on artificial reefs was mainly due to adult immigration. Piscivores were much more abundant in the fall than in the winter or spring on artificial reefs, but had low and stable abundance throughout the year in natural habitats. It is likely that the decreased winter and spring abundance of fish on the artificial reefs resulted from both predation and emigration. These results indicate that large artificial reefs can support diverse and abundant coral and fish communities. However, these communities differ structurally and functionally from those in natural habitats, and they should not be considered as replacements for natural coral and fish communities. © Springer-Verlag 2009

Wakefield damping for the CLIC crab cavity

A crab cavity is required in the CLIC to allow effective head-on collision of bunches at the IP. A high operating frequency is preferred as the deflection voltage required for a given rotation angle and the RF phase tolerance for a crab cavity are inversely proportional to the operating frequency. The short bunch spacing of the CLIC scheme and the high sensitivity of the crab cavity to dipole kicks demand very high damping of the inter-bunch wakes, the major contributor to the luminosity loss of colliding bunches. This paper investigates the nature of the wakefields in the CLIC crab cavity and the possibility of using various damping schemes to suppress them effectively

Integrated electrical and mechanical modelling of integrated-full-electric-propulsion systems

Integrated Full Electric Propulsion (IFEP) systems are the subject of much interest at present. Current research is focused on analysing and improving aspects of subsystem and system performance. However, there is a great need to look more widely at the `multi-physics' problem of characterising the dynamic interactions between the electrical and mechanical systems. This paper will discuss the changing nature of modelling and simulation to aid research into IFEP systems, outlining the alternative angle taken by the Advanced Marine Electrical Propulsion Systems (AMEPS) project to characterise and investigate electrical-mechanical system interactions. The paper will describe this approach and highlight the unique challenges associated with the problem, discussing the suitable methods that will be adopted to address these challenges. Finally, an overview of the present and future research opportunities facilitated via the AMEPS project will be presented

The global transformation of geomorphology

This chapter reviews the various developments in geomorphology in terms of institutions, journals, textbooks, research stations, etc. Among the institutions discussed are the Binghamton Geomorphology Symposium, the Geological Society of America Quaternary Geology and Geomorphology Division, the Association of American Geographers Geomorphology Specialty Group, the British Geomorphological Research Group, the IGU Commission on Measurements, Theory and Application in Geomorphology (COMTAG), the International Association of Geomorphologists, the European Geosciences Union (EGU), the American Geophysical Union (AGU), the International Quaternary Association, and the International Conference on Aeolian Research. Many countries established their own national bodies. A number of new journals appeared, including Catena, Earth Surface Processes and Landforms, Géomorphologie, and Geomorphology. In addition, during the closing decades of the twentieth century there was a proliferation of textbooks in geomorphology. One development was that geomorphological research was promoted by the establishment of research stations. These permitted long-term monitoring and provided bases for sustained investigations. The study of fluvial processes was much encouraged in the United States at USDA Forest Service research basins (known as ‘watersheds’ in the USA) such as the Hubbard Brook Experimental Forest (New Hampshire), Coweeta Hydrologic Laboratory (North Carolina) and the H.J. Andrews Experimental Forest (Oregon). The Royal Geographical Society (with the Institute of British Geographers) organized ambitious research projects in collaboration with host nations. Various US government departments supported much geomorphological research in various parts of the world. Some European countries fostered overseas geomorphological research and created missions. Notable was the work of ORSTOM (Office de la Recherche Scientifique et Technique Outre-mer) in former francophone colonies. In the post-war years, and as independence approached and then occurred, new universities were established in Africa. These employed expatriate geomorphologists and also trained up a new generation of indigenous scholars. The decades since the 1960s have been a period of space exploration and the development of remote sensing. This has had important implications for geomorphology. The period also saw the onset of the digital age and the beginning of the World Wide Web's influence on teaching and research. Applied research became increasingly important. A major cause for international and cross-disciplinary co-operation during the period was the emergence of geoarchaeology. Finally, since the 1950s, an increasing number of women have made important contributions to the discipline

Characteristics of Pump Performance in Major Irrigated Areas of California

Well pump tests (12,876) in three Central California groundwater basins were characterized and described according to their spatial distribution. The average overall pumping plant efficiency (wire-water, not including column losses and velocity head) was about 56%. Characteristics such as drawdown, total dynamic heads, kW, and flow rate vary greatly between pumps within and between sub-basins. This is the first well pump characterization of its type in California, although irrigation pump tests have been conducted for over 70 years in California. This paper provides a summary of the spatial variation of well pump performance and characteristics