Cavity solitons as pixels in semiconductor microcavities

Cavity solitons are localized intensity peaks that can form in a homogeneous background of radiation. They are generated by shining laser pulses into optical cavities that contain a nonlinear medium driven by a coherent field (holding beam). The ability to switch cavity solitons on and off and to control their location and motion by applying laser pulses makes them interesting as potential 'pixels' for reconfigurable arrays or all-optical processing units. Theoretical work on cavity solitons has stimulated a variety of experiments in macroscopic cavities and in systems with optical feedback. But for practical devices, it is desirable to generate cavity solitons in semiconductor structures, which would allow fast response and miniaturization. The existence of cavity solitons in semiconductor microcavities has been predicted theoretically, and precursors of cavity solitons have been observed, but clear experimental realization has been hindered by boundary-dependence of the resulting optical patterns-cavity solitons should be self-confined. Here we demonstrate the generation of cavity solitons in vertical cavity semiconductor microresonators that are electrically pumped above transparency but slightly below lasing threshold. We show that the generated optical spots can be written, erased and manipulated as objects independent of each other and of the boundary. Numerical simulations allow for a clearer interpretation of experimental results.     

Synaptic defects in ataxia mice result from a mutation in Usp14, encoding a ubiquitin-specific protease

Mice that are homozygous with respect to a mutation (ax(J)) in the ataxia (ax) gene develop severe tremors by 2-3 weeks of age followed by hindlimb paralysis and death by 6-10 weeks of age. Here we show that ax encodes ubiquitin-specific protease 14 (Usp14). Ubiquitin proteases are a large family of cysteine proteases that specifically cleave ubiquitin conjugates. Although Usp14 can cleave a ubiquitin-tagged protein in vitro, it is unable to process polyubiquitin, which is believed to be associated with the protein aggregates seen in Parkinson disease, spinocerebellar ataxia type 1 (SCA1; ref. 4) and gracile axonal dystrophy (GAD). The physiological substrate of Usp14 may therefore contain a mono-ubiquitin side chain, the removal of which would regulate processes such as protein localization and protein activity. Expression of Usp14 is significantly altered in ax(J)/ax(J) mice as a result of the insertion of an intracisternal-A particle (IAP) into intron 5 of Usp14. In contrast to other neurodegenerative disorders such as Parkinson disease and SCA1 in humans and GAD in mice, neither ubiquitin-positive protein aggregates nor neuronal cell loss is detectable in the central nervous system (CNS) of ax(J) mice. Instead, ax(J) mice have defects in synaptic transmission in both the central and peripheral nervous systems. These results suggest that ubiquitin proteases are important in regulating synaptic activity in mammals.     

Rapid regulation of steroidogenesis by mitochondrial protein import

Most mitochondrial proteins are synthesized on cytoplasmic ribosomes and imported into mitochondria. The imported proteins are directed to one of four submitochondrial compartments--the outer mitochondrial membrane, the inner mitochondrial membrane, the intramembraneous space, or the matrix--where the protein then functions. Here we show that the steroidogenic acute regulatory protein (StAR), a mitochondrial protein required for stress responses, reproduction, and sexual differentiation of male fetuses, exerts its activity transiently at the outer mitochondrial membrane rather than at its final resting place in the matrix. We also show that its residence time at this outer membrane and its activity are regulated by its speed of mitochondrial import. This may be the first example of a mitochondrial protein exerting its biological activity in a compartment other than that to which it is finally targeted. This system enables steroidogenic cells to initiate and terminate massive levels of steroidogenesis within a few minutes, permitting the rapid regulation of serum steroid hormone concentrations.     

Genetic variation in the 5q31 cytokine gene cluster confers susceptibility to Crohn disease

Linkage disequilibrium (LD) mapping provides a powerful method for fine-structure localization of rare disease genes, but has not yet been widely applied to common disease. We sought to design a systematic approach for LD mapping and apply it to the localization of a gene (IBD5) conferring susceptibility to Crohn disease. The key issues are: (i) to detect a significant LD signal (ii) to rigorously bound the critical region and (iii) to identify the causal genetic variant within this region. We previously mapped the IBD5 locus to a large region spanning 18 cM of chromosome 5q31 (P<10(-4)). Using dense genetic maps of microsatellite markers and single-nucleotide polymorphisms (SNPs) across the entire region, we found strong evidence of LD. We bound the region to a common haplotype spanning 250 kb that shows strong association with the disease (P< 2 x 10(-7)) and contains the cytokine gene cluster. This finding provides overwhelming evidence that a specific common haplotype of the cytokine region in 5q31 confers susceptibility to Crohn disease. However, genetic evidence alone is not sufficient to identify the causal mutation within this region, as strong LD across the region results in multiple SNPs having equivalent genetic evidence-each consistent with the expected properties of the IBD5 locus. These results have important implications for Crohn disease in particular and LD mapping in general.     

Distribution records and comments on mammals in western South Dakota

The mammal fauna of western South Dakota is imperfectly known; in particular there is a notable paucity of data from Indian reservations in the region. We collected mammals from January 2003 through May 2006 using a variety of standard methodologies, including trapping with snap-traps and Macabee traps, shooting, and salvaging road- and hunter-killed animals. Herein we provide 23 specimen-based county records representing 17 species of mammals. In addition, a photo record constitutes the first report of Dasypus novemcinctus from South Dakota and the northernmost record in the United States. The possible local extirpation of Marmota flaviventris in the southern Black Hills is discussed.     

Managing a complex exotic vegetation program in Yellowstone National Park

The number of documented exotic plants in Yellowstone National Park has increased from 85 known in 1986 to over 185 today. Exotic plants are substantially impacting the parks natural and cultural resources and are a high management priority. We have adopted an integrated weed management approach with regard to exotic vegetation, emphasizing prevention, education, early detection and eradication, control, and, to a lesser degree, monitoring. The program involves over 140 staff with program expenditures averaging approximately $190,000 annually. Prevention actions include requiring approved gravel on construction projects; banning hay in the backcountry and allowing transport of only certified weed-seed-free hay through Yellowstone; requiring construction equipment to be pressurecleaned prior to entering the park; and native species revegetation after road, housing, and other construction projects have disturbed ground. Over 4500 acres, primarily along roadsides and in developed areas, are surveyed annually in early detection efforts with emphasis placed on eradicating small, new infestations of highly invasive species such as sulfur cinquefoil ( Potentilla recta L.) and leafy spurge ( Euphorbia esula L.). Control efforts focus on about 30 priority species, such as spotted knapweed ( Centaurea maculosa Lam.), oxeye daisy ( Chrysanthemum leucanthemum L.), and hoary cress ( Cardaria draba [L.] Desv.) using chemical, mechanical, and cultural techniques. A total of 2027 acres were treated during 1998, whereas control efforts for 12 species occurred on 2596 acres during the previous 3-year period, 1995-1997. Strong and expanding partnerships with other federal, state, and local agencies and private companies contribute to management efforts within the park. Future program goals emphasize increases in base funding to ensure continued weed management efforts as well as expanding survey, monitoring, and reclamation efforts. Ultimately, a more rigorous assessment of program effectiveness is desired.     

Relationship of western juniper stem conducting tissue and basal circumference to leaf area and biomass

The ability to measure leaf area and biomass on a plant community basis has many important ecological applications. These include quantification of gas exchange, use of water resources on the site, nutrient pools, and construction of models simulating production and resource allocation. To test a nondestructive technique for estimating leaf area and leaf biomass of western juniper ( Juniperus occidentalis Hook.), sapwood area and basal circumference were evaluated as predictors of total leaf biomass and leaf area. Nineteen trees, ranging in size from 9.0 to 263 cm in circumference, were destructively sampled. The entire leaf biomass was harvested and measured, and regression equations were developed. Both sapwood area and basal circumference significantly (P < .01) correlated with projected leaf area and leaf biomass (r values = 0.98).     

Taphonomy and significance of Jefferson's ground sloth (Xenarthra: Megalonychidae) from Utah

While a variety of mammalian megafauna have been recovered from sediments associated with Lake Bonneville, Utah, sloths have been notably rare. Three species of ground sloth, Megalonyx jeffersonii, Paramylodon harlani, and Nothrotheriops shastensis , are known from the western United States during the Pleistocene. Yet all 3 are rare in the Great Basin, and the few existing records are from localities on the basin margin. The recent discovery of a partial skeleton of Megalonyx jeffersonii at Point-of-the-Mountain, Salt Lake County, Utah, fits this pattern and adds to our understanding of the distribution and ecology of this extinct species. Its occurrence in Lake Bonneville shoreline deposits permits a reasonable age determination of between 22 and 13 ka.     

Using the Acropora digitifera genome to understand coral responses to environmental change

Despite the enormous ecological and economic importance of coral reefs, the keystone organisms in their establishment, the scleractinian corals, increasingly face a range of anthropogenic challenges including ocean acidification and seawater temperature rise. To understand better the molecular mechanisms underlying coral biology, here we decoded the approximately 420-megabase genome of Acropora digitifera using next-generation sequencing technology. This genome contains approximately 23,700 gene models. Molecular phylogenetics indicate that the coral and the sea anemone Nematostella vectensis diverged approximately 500 million years ago, considerably earlier than the time over which modern corals are represented in the fossil record (～240 million years ago). Despite the long evolutionary history of the endosymbiosis, no evidence was found for horizontal transfer of genes from symbiont to host. However, unlike several other corals, Acropora seems to lack an enzyme essential for cysteine biosynthesis, implying dependency of this coral on its symbionts for this amino acid. Corals inhabit environments where they are frequently exposed to high levels of solar radiation, and analysis of the Acropora genome data indicates that the coral host can independently carry out de novo synthesis of mycosporine-like amino acids, which are potent ultraviolet-protective compounds. In addition, the coral innate immunity repertoire is notably more complex than that of the sea anemone, indicating that some of these genes may have roles in symbiosis or coloniality. A number of genes with putative roles in calcification were identified, and several of these are restricted to corals. The coral genome provides a platform for understanding the molecular basis of symbiosis and responses to environmental changes.