10,539 research outputs found
Study of cosmic dust particles on board LDEF: The FRECOPA experiments AO138-1 and AO138-2
Two experiments, within the French Cooperative Payload (FRECOPA) and devoted to the detection of cosmic dust, were flown on the LDEF. A variety of sensors and collecting devices have made possible the study of impact processes on materials of technological interest. Preliminary examination of hypervelocity impact features gives valuable data on size distribution and nature of interplanetary dust particles in low earth orbit, within the 0.5 to 300 micrometer size range. Most of the events detected on the trailing face of LDEF are expected to be the result of impacts of meteoritic particles only. So far, chemical analysis of craters by EDS clearly shows evidence of elements (Na, Mg, Si, S, Ca, and Fe) consistent with cosmic origin. Systematic occurrence of C and O in crater residues is an important result, to be compared with the existence of CHON particles detected in P-Halley comet nucleus. Crater size distribution is in good agreement with results from other dust experiments flown on LDEF. However, no crater smaller than 1.5 micron was observed, thus suggesting a cutoff in the near earth particle distribution. Possible origin and orbital evolution of micrometeoroids is discussed
The effect of the number of response cycles on the behaviour of reinforced concrete elements subject to cyclic loading
The development of damage in reinforced concrete (RC) structures is a cumulative process. Some damage
indices used to quantify damage make use of the number of response cycles as an Engineering Demand
Parameter (EDP) relating with damage development. Other indices make use of deformation in terms of
displacement or chord rotation. These functions are generally a function of whether the response is monotonic or
cyclic, and are insensitive to the number of major deflection cycles leading to that state of damage. Many such
relations are derived from experimental data from low-cycle fatigue tests performed on RC elements. The
loading in such tests generally consists of either a monotonic increase in load or a gradually increasing cyclic
load. Since damage development is a cumulative process, and hence depends on the load history, the loading
pattern in low-cycle fatigue tests for assessment purposes should reflect the response of an earthquake. This
paper will discuss a procedure to determine a loading history for cyclic tests, based on earthquake demands. The
preliminary results of a campaign of low-cycle fatigue tests on RC elements to investigate the effect of using
different load histories are also discussed
Low cycle fatigue tests of reinforced concrete columns and joints built with ribbed reinforcement and plain stirrups
The majority of existing reinforced concrete (RC) buildings were built prior to the introduction of seismic codes.
As observed in various recent earthquakes, due to their lack of structural capacity and ductility such structures
are very vulnerable and have suffered considerable damage. The number of cyclic tests that have been carried
out to investigate the behaviour of RC components with detailing typical of these buildings is very limited. Such
tests are very relevant for seismic vulnerability assessment purposes. In this paper, a low-cycle fatigue testing
campaign on RC columns and connections specifically devised to investigate various physical parameters that
affect damage development, is presented. The campaign consists of 19 columns and 7 beam-column connections.
Some of the preliminary results and observations are presented and discussed
Review of the financial and medicolegal implications of nasal fractures seen at St Luke’s Hospital
Simple nasal bone fractures are the third most common type of all fractures leading to numerous patient visits at the Accident & Emergency department. Nasal fractures are commonly over-investigated in St Luke’s hospital leading to a substantial financial burden on our health system. In this article we review the frequency of simple nasal fractures as well as the necessity or otherwise of nasal x-ray imaging in addition to the financial and health consequences that result from nasal x-ray imaging. These issues are also discussed from a legal perspective.peer-reviewe
Hepatitis B immunisation : a survey of surgeons and theatre nurses
Acute viral hepatitis remains a serious condition. Its long-term sequelae include cirrhosis and hepatocellular carcinoma. Health workers constitute a high-risk group for contracting hepatitis B. A group of clinicians associated with invasive procedures and nurses working in operating theatres were invited to answer a confidential questionnaire concerning hepatitis B immunisation and the use of protective measures. A self-administered confidential questionnaire was sent to 152 clinicians and 97 theatre nurses, of whom 82 and 74 respectively responded, giving an overall response rate of 63 %. Whilst 91% of respondents considered their speciality as being of high risk for hepatitis B only 63% of them were fully immunised and of these only 51% had had their immunity tested. Out of those who checked their antibody status 19% did so following a needle stick injury. 60% of our respondents had had a needle stick injury over the past year. Even so barrier precaution techniques were used infrequently with only 17% always or at least frequently using double gloving and 10% wearing a visor during operations. Some respondents also commented on the poor availability of resources such as impermeable gowns or blunt needles which are established precautions against contamination from hepatitis B.peer-reviewe
VLA Observations of the Infrared Dark Cloud G19.30+0.07
We present Very Large Array observations of ammonia (NH3) (1,1), (2,2), and
CCS (2_1-1_0) emission toward the Infrared Dark Cloud (IRDC) G19.30+0.07 at
~22GHz. The NH3 emission closely follows the 8 micron extinction. The NH3 (1,1)
and (2,2) lines provide diagnostics of the temperature and density structure
within the IRDC, with typical rotation temperatures of ~10 to 20K and NH3
column densities of ~10^15 cm^-2. The estimated total mass of G19.30+0.07 is
~1130 Msun. The cloud comprises four compact NH3 clumps of mass ~30 to 160
Msun. Two coincide with 24 micron emission, indicating heating by protostars,
and show evidence of outflow in the NH3 emission. We report a water maser
associated with a third clump; the fourth clump is apparently starless. A
non-detection of 8.4GHz emission suggests that the IRDC contains no bright HII
regions, and places a limit on the spectral type of an embedded ZAMS star to
early-B or later. From the NH3 emission we find G19.30+0.07 is composed of
three distinct velocity components, or "subclouds." One velocity component
contains the two 24 micron sources and the starless clump, another contains the
clump with the water maser, while the third velocity component is diffuse, with
no significant high-density peaks. The spatial distribution of NH3 and CCS
emission from G19.30+0.07 is highly anti-correlated, with the NH3 predominantly
in the high-density clumps, and the CCS tracing lower-density envelopes around
those clumps. This spatial distribution is consistent with theories of
evolution for chemically young low-mass cores, in which CCS has not yet been
processed to other species and/or depleted in high-density regions.Comment: 29 pages, 9 figures, accepted for publication by ApJ. Please contact
the authors for higher resolution versions of the figure
Mean first passage time analysis reveals rate-limiting steps, parallel pathways and dead ends in a simple model of protein folding
We have analyzed dynamics on the complex free energy landscape of protein
folding in the FOLD-X model, by calculating for each state of the system the
mean first passage time to the folded state. The resulting kinetic map of the
folding process shows that it proceeds in jumps between well-defined, local
free energy minima. Closer analysis of the different local minima allows us to
reveal secondary, parallel pathways as well as dead ends.Comment: 7 page
Deriving a systematic approach to changeable manufacturing system design
It has long been argued that Factories are long life and complex products. The complexity of designing factories, and their underlying manufacturing systems, is further amplified when dealing with continuously changing customer demands. At the same time, due to research fragmentation, little if any scientific explanations are available supporting and exploiting the paradigm that "factories are products". In order to address this weakness, this paper presents research results arising from a comparative analysis of systematic "product design" and "manufacturing system design" approaches. The contribution emerging from this research is an integrated systematic design approach to changeable manufacturing systems, based on scientific concepts founded upon product design theories, and is explained through a case study in the paper. This research is part of collaboration between the CERU University of Malta and IAO Fraunhofer aimed at developing a digital decision support tool for planning changeable manufacturing systems.peer-reviewe
Report on the excavation of a Punic tomb
On 19th November 2001, while two of us (DB, NJC)
were preparing a drawn record of the Punic tomb
that is situated on Bajda Ridge, Xemxija, a small
ceramic bowl (100211) was uncovered from below
a few centimetres of soil that covered the inner part
of the threshold to the rock-cut chamber (Fig. 1).
An official from the Museums Department was
informed of the discovery on the same day and a
site inspection was carried out. It was realised that
more artefacts could lie undisturbed within the
chamber and a decision was taken to excavate the
deposit. Authorisation for the Department of
Classics and Archaeology, University of Malta, to
undertake the excavation was received from the
Director, Museums Department, and the excavation
was completed on the 22nd November.
The tomb is located on the ridge, near a path that
diverges eastwards from the track that links Pwales
valley to the Mistra valley. It is cut in the Upper
Coralline limestone that outcrops in the area on a
North-South axis and consists of a sub-rectangular
chamber that is reached through a low entrance at
the bottom of a rectangular shaft (Fig. 1).
The tomb appears in an inventory for the first time
in 1996 when it was listed in the survey of
archaeological sites prepared by Malta University
Services for the Planning Authority by Anthony
Bonanno in connection with the preparation of the
North-West local plan for Malta. The tomb had been
examined and photographed by one of us (NCV) in
1992. At the time, it was littered with debris and it
was only with difficulty that a view of the chamber
could be achieved through the entrance that was
partly concealed by an irregular blocking stone. Late
in 2000, members of the St Paul's Bay Heritage
Group lifted the debris from the trench and cleared
the area around the site.peer-reviewe
The utilization of an infrared imaging system as a cooling slot blockage detector in the inspection of a transpiration cooled nozzle
A comprehensive examination of the 8 foot temperature tunnel's transpiration cooled nozzle was completed using an infrared imaging radiometer to locate regions of cooling flow irregularities caused by obstruction of three or more adjacent cooling slots. Restrictions in the cooling flow were found and cataloged. Blockages found were due primarily to the presence of residual phosphoric acid being discharged from some of the cooling slots. This acid was used during construction of the nozzle components and was to have been purged prior to its delivery to the NASA Langley Research Center (LaRC). In addition, a radial displacement of one selection of discs located in the spool piece was inspected and cataloged for future reference. There did not seem to be a serious restriction of flow in this defect, but evidence from the infrared images indicated reduced slot activity within the gouge. The radiometer survey uncovered regions where closer inspection is recommended but did not cover the entire surface area of the three nozzle subsections due to equipment limitations. A list of areas with suspected problems is included in Appendix A
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