5,030 research outputs found
Development of an evaluation technique for strapdown guidance systems Interim scientific report
Evaluation technique to measure performance of strapdown guidance systems designed for unmanned interplanetary mission
Crystal structures of trypanosoma brucei oligopeptidase B broaden the paradigm of catalytic regulation in prolyl oligopeptidase family enzymes
Oligopeptidase B cleaves after basic amino acids in peptides up to 30 residues. As a virulence factor in bacteria and trypanosomatid pathogens that is absent in higher eukaryotes, this is a promising drug target. Here we present ligand-free open state and inhibitor-bound closed state crystal structures of oligopeptidase B from Trypanosoma brucei, the causative agent of African sleeping sickness. These (and related) structures show the importance of structural dynamics, governed by a fine enthalpic and entropic balance, in substrate size selectivity and catalysis. Peptides over 30 residues cannot fit the enzyme cavity, preventing the complete domain closure required for a key propeller Asp/Glu to fix the catalytic His and Arg in the catalytically competent conformation. This size exclusion mechanism protects larger peptides and proteins from degradation. Similar bacterial prolyl endopeptidase and archael acylaminoacyl peptidase structures demonstrate this mechanism is conserved among oligopeptidase family enzymes across all three domains of life
The Spectral Evolution of Transient Anomalous X-ray Pulsar XTE J1810--197
(Abridged) We present a multi-epoch spectral study of the Transient Anomalous
X-ray Pulsar XTE J1810-197 obtained with the XMM X-ray telescope. Four
observations taken over the course of a year reveal strong spectral evolution
as the source fades from outburst. The origin of this is traced to the
individual decay rates of the pulsar's spectral components. A 2-T fit at each
epoch requires nearly constant temperatures of kT=0.25 & 0.67 keV while the
component luminosities decrease exponentially with tau=900 & 300d,
respectively. One possible interpretation is that the slowly decaying cooler
component is the radiation from a deep heating event that affected a large
fraction of the crust, while the hotter component is powered by external
surface heating at the foot-points of twisted magnetic field lines, by
magnetospheric currents that are decaying more rapidly. The energy-dependent
pulse profile of XTE J1810-197 is well modeled at all epochs by the sum of a
sine and triangle function. These profiles peak at the same phase, suggesting a
concentric surface emission geometry. The spectral and pulse evolution together
argue against the presence of a significant ``power-law'' contribution to the
X-ray spectrum below 8 keV. The extrapolated flux is projected to return to the
historic quiescent level, characterized by an even cooler blackbody spectrum,
by the year 2007.Comment: 12 pages, 6 Figures, Latex, emulateapj. To appear in the
Astrophysical Journa
Long term hard X-ray variability of the anomalous X-ray pulsar 1RXS J170849.0-400910 discovered with INTEGRAL
We report on a multi-band high-energy observing campaign aimed at studying
the long term spectral variability of the Anomalous X-ray Pulsar (AXP) 1RXS
J170849.0-400910, one of the magnetar candidates. We observed 1RXS
J170849.0-400910 in Fall 2006 and Spring 2007 simultaneously with Swift/XRT, in
the 0.1-10 keV energy range, and with INTEGRAL/IBIS, in the 20-200 keV energy
range. Furthermore, we also reanalyzed, using the latest calibration and
software, all the publicly available INTEGRAL data since 2002, and the soft
X-ray data starting from 1999 taken using BeppoSAX, Chandra, XMM, and
Swift/XRT, in order to study the soft and hard X-ray spectral variability of
1RXS J170849.0-400910. We find a long-term variability of the hard X-ray flux,
extending the hardness-intensity correlation proposed for this source over 2
orders of magnitude in energy.Comment: 5 pages, 2 figures, accepted for publication in Astronomy &
Astrophysics main journa
Hybrid Inspection Robot for Indoor and Outdoor Surveys
In this paper, simulation and experimental tests are reported for a hybrid robot being used for indoor and outdoor inspections. Automatic or tele-operated surveys can be performed by mobile robots, which represent the most efficient solution in terms of power consumption, control, robustness, and overall costs. In the context of structures and infrastructure inspection, robots must be able to move on horizontal or sloped surfaces and overpass obstacles. In this paper, the mechatronic design, simulations, and experimental activity are proposed for a hybrid robot being used for indoor and outdoor inspections, when the environmental conditions do not allow autonomous navigation. In particular, the hybrid robot is equipped with external and internal sensors to acquire information on the main structural elements, avoiding the need for experienced personnel being directly inside the inspection site, taking information from the environment and aiding the pilot to understand the best maneuvers/decisions to take. Given the current state of research and shortcomings worldwide, this paper discusses inspection robots taking into account the main issues in their use, functionality and standard systems, and how internal sensors can be set in order to improve inspection robots’ performances. On this basis, an illustrative study case is proposed
Design and Development of an Inspection Robotic System for Indoor Applications
The inspection and monitoring of industrial sites, structures, and infrastructure are important issues for their sustainability and further maintenance. Although these tasks are repetitive and time consuming, and some of these environments may be characterized by dust, humidity, or absence of natural light, classical approach relies on large human activities. Automatic or robotic solutions can be considered useful tools for inspection because they can be effective in exploring dangerous or inaccessible sites, at relatively low-cost and reducing the time required for the relief. The development of a paradigmatic system called Inspection Robotic System (IRS) is the main objective of this paper to demonstrate the feasibility of mechatronic solutions for inspection of industrial sites. The development of such systems will be exploited in the form of a tool kit to be flexible and installed on a mobile system, in order to be used for inspection and monitoring, possibly introducing high efficiency, quality and repetitiveness in the related sector. The interoperability of sensors with wireless communication may form a smart sensors tool kit and a smart sensor network with powerful functions to be effectively used for inspection purposes. Moreover, it may constitute a solution for a broad range of scenarios spacing from industrial sites, brownfields, historical sites or sites dangerous or difficult to access by operators. First experimental tests are reported to show the engineering feasibility of the system and interoperability of the mobile hybrid robot equipped with sensors that allow real-time multiple acquisition and storage
From the emotional integration to the cognitive construction: the developmental approach of Turtle Project in children with autism spectrum disorder
Background: Children with autism spectrum disorder show a deficit in neurobiological processes. This deficit
hinders the development of intentional behavior and appropriate problem-solving, leading the child to implement
repetitive and stereotyped behaviors and to have difficulties in reciprocal interactions, empathy and in the
development of a theory of mind. The objective of this research is to verify the effectiveness of a relationship-based
approach on the positive evolution of autistic symptoms.
Method: A sample of 80 children with autism spectrum disorder was monitored during the first four years of
therapy, through a clinical diagnostic assessment at the time of intake and then in two follow-up.
Results: The results showed that through the Autism Diagnostic Observation Schedule it is possible to
assess the socio-relational key elements on which the therapy is based. There was evidence, in fact, of significant
improvements after two and four years of therapy, both for children with severe autistic symptoms and for those in
autistic spectrum.
Conclusions: Socio-relational aspects represent the primary element on which work in therapy with autistic
children and can be considered as indicators of a positive evolution and prognosis that will produce improvements
even in the cognitive are
Observations of one young and three middle-aged -ray pulsars with the Gran Telescopio Canarias
We used the 10.4m Gran Telescopio Canarias to search for the optical
counterparts to four isolated -ray pulsars, all detected in the X-rays
by either \xmm\ or \chan\ but not yet in the optical. Three of them are
middle-aged pulsars -- PSR\, J1846+0919 (0.36 Myr), PSR\, J2055+2539 (1.2 Myr),
PSR\, J2043+2740 (1.2 Myr) -- and one, PSR\, J1907+0602, is a young pulsar
(19.5 kyr). For both PSR\, J1907+0602 and PSR\, J2055+2539 we found one object
close to the pulsar position. However, in both cases such an object cannot be a
viable candidate counterpart to the pulsar. For PSR\, J1907+0602, because it
would imply an anomalously red spectrum for the pulsar and for PSR\, J2055+2539
because the pulsar would be unrealistically bright () for the
assumed distance and interstellar extinction. For PSR\, J1846+0919, we found no
object sufficiently close to the expected position to claim a possible
association, whereas for PSR\, J2043+2740 we confirm our previous findings that
the object nearest to the pulsar position is an unrelated field star. We used
our brightness limits (), the first obtained with a
large-aperture telescope for both PSR\, J1846+0919 and PSR\, J2055+2539, to
constrain the optical emission properties of these pulsars and investigate the
presence of spectral turnovers at low energies in their multi-wavelength
spectra.Comment: 10 pages, 11 figures, accpted for publication in MNRA
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