313 research outputs found

    Technology requirements for post-1985 communications satellites

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    The technical and functional requirements for commercial communication satellites are discussed. The need for providing quality service at an acceptable cost is emphasized. Specialized services are postulated in a needs model which forecasts future demands. This needs model is based upon 322 separately identified needs for long distance communication. It is shown that the 1985 demand for satellite communication service for a domestic region such as the United States, and surrounding sea and air lanes, may require on the order of 100,000 MHz of bandwith. This level of demand can be met by means of the presently allocated bandwidths and developing some key technologies. Suggested improvements include: (1) improving antennas so that high speed switching will be possible; (2) development of solid state transponders for 12 GHz and possibly higher frequencies; (3) development of switched or steered beam antennas with 10 db or higher gain for aircraft; and (4) continued development of improved video channel compression techniques and hardware

    Technology requirements for communication satellites in the 1980's

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    The key technology requirements are defined for meeting the forecasted demands for communication satellite services in the 1985 to 1995 time frame. Evaluation is made of needs for services and technical and functional requirements for providing services. The future growth capabilities of the terrestrial telephone network, cable television, and satellite networks are forecasted. The impact of spacecraft technology and booster performance and costs upon communication satellite costs are analyzed. Systems analysis techniques are used to determine functional requirements and the sensitivities of technology improvements for reducing the costs of meeting requirements. Recommended development plans and funding levels are presented, as well as the possible cost saving for communications satellites in the post 1985 era

    Citron Kinase, a RhoA Effector, Enhances HIV-1 Virion Production by Modulating Exocytosis

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    RhoGTPases play important roles in the regulation of protein transport and membrane recycling. Little is known, however, about how RhoGTPases affect HIV-1 virion production, which is dependent on the endosomal sorting pathway. We report that ectopic expression of citron kinase (citron-K), a RhoA effector, preferentially enhances HIV-1 virion production. Depletion of endogenous citron-K inhibits HIV-1 virion production. Citron-N, which lacks the kinase domain, also enhances HIV-1 virion production. The leucine zipper, Rho-binding and zinc finger domains of citron-N are necessary for the enhancement activity. Citron-K also enhances murine leukemia virion production and the HIV-1 late domain is not required for the citron-K-mediated enhancement. Ectopic expression of citron-K leads to the formation of cytoplasmic structures containing citron-K and HIV-1 Gag proteins. HIV-1 and citron-K cooperatively enhance acidic endosome and lysosome compartments. Finally, citron-K promotes exocytosis of microvesicles or exosomes that co-purify with HIV-1 virions. We conclude that citron-K enhances HIV-1 virion production by stimulating the endosomal compartments and exocytosis

    Decision-support system for safety and security assessment and management in smart cities

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    Counter-terrorism measures and preparedness play a critical role in securing mass gatherings, soft targets, and critical infrastructures within urban environments. This paper introduces a comprehensive Decision Support System developed as part of the S4AllCitites project, designed to seamlessly integrate with existing legacy systems in Smart Cities. The system encompasses urban pedestrian and vehicular evacuation, incorporating predictive models to anticipate the progression of incendiary and mass shooting attacks, alongside a probabilistic model for threat assessment in the case of improvised explosive devices. A notable achievement of this research is the successful implementation and deployment of the system in operational environments through pilot studies. It empowers public and private security operators with real time decision support capabilities during both prevention and intervention stages of potential attacks. The decision support information provided encompasses various aspects, including optimal evacuation strategies, estimated egress times, pedestrian movement profiles, probability assessments, and the potential impact of different terrorist threats in terms of casualties. Additionally, the system offers real-time insights into the status of the traffic network under normal and unusual conditions, enabling efficient emergency management throughout its progression. This includes the ability to identify optimal intervention routes and assess the impact of anomalous traffic resulting from evacuations

    Single Molecule Conformational Memory Extraction: P5ab RNA Hairpin

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    Extracting kinetic models from single molecule data is an important route to mechanistic insight in biophysics, chemistry, and biology. Data collected from force spectroscopy can probe discrete hops of a single molecule between different conformational states. Model extraction from such data is a challenging inverse problem because single molecule data are noisy and rich in structure. Standard modeling methods normally assume (i) a prespecified number of discrete states and (ii) that transitions between states are Markovian. The data set is then fit to this predetermined model to find a handful of rates describing the transitions between states. We show that it is unnecessary to assume either (i) or (ii) and focus our analysis on the zipping/unzipping transitions of an RNA hairpin. The key is in starting with a very broad class of non-Markov models in order to let the data guide us toward the best model from this very broad class. Our method suggests that there exists a folding intermediate for the P5ab RNA hairpin whose zipping/unzipping is monitored by force spectroscopy experiments. This intermediate would not have been resolved if a Markov model had been assumed from the onset. We compare the merits of our method with those of others

    Exposure of bakery and pastry apprentices to airborne flour dust using PM2.5 and PM10 personal samplers

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    <p>Abstract</p> <p>Background</p> <p>This study describes exposure levels of bakery and pastry apprentices to flour dust, a known risk factor of occupational asthma.</p> <p>Methods</p> <p>Questionnaires on work activity were completed by 286 students. Among them, 34 performed a series of two personal exposure measurements using a PM<sub>2.5 </sub>and PM<sub>10 </sub>personal sampler during a complete work shift, one during a cold ("winter") period, and the other during a hot ("summer") period.</p> <p>Results</p> <p>Bakery apprentices experience greater average PM<sub>2.5 </sub>and PM<sub>10 </sub>exposures than pastry apprentices (p < 0.006). Exposure values for both particulate fractions are greater in winter (average PM<sub>10 </sub>values among bakers = 1.10 mg.m<sup>-3 </sup>[standard deviation: 0.83]) than in summer (0.63 mg.m<sup>-3 </sup>[0.36]). While complying with current European occupational limit values, these exposures exceed the ACGIH recommendations set to prevent sensitization to flour dust (0.5 mg.m<sup>-3</sup>). Over half the facilities had no ventilation system.</p> <p>Conclusion</p> <p>Young bakery apprentices incur substantial exposure to known airways allergens, a situation that might elicit early induction of airways inflammation.</p

    Four functional roles for case studies in emerging adulthood research

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    Case studies have four functional roles which, if more widely embraced, can help to advance theory and methodology in the study of emerging adults. These functions are: case-based theory development, individual-level prediction testing, theory exemplification, and idiographic psychobiography. We describe these functions and provide examples of how each one can add depth, richness and rigour to the burgeoning theory and research on emerging adulthood. We also discuss specifiability (the capacity of a theory to make predictions about, explain and interpret individuals) as a criterion of validity, to be considered as equivalent in status to the external validity criterion of generalizability. Finally we consider the protocols for case study sampling, including intensity sampling, deviant case sampling and significant case sampling
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