1,084 research outputs found
Temporary Jobs: Stepping Stones or Dead Ends?
In Britain about 7% of male employees and 10% of female employees are in temporary jobs. In contrast to much of continental Europe - with stricter employment protection provisions - this proportion has been relatively stable over the 1990s. Using data from the British Household Panel Survey, and informed by relevant theory relating to probation, sorting and human capital investment, we find that temporary workers report lower levels of job satisfaction, receive less work-related training, and are less well-paid than their counterparts in permanent employment. However, there is some evidence that fixed-term contracts are a stepping stone to permanent work. Women (but not men) who start in fixed-term employment and move to permanent jobs fully catch up to those who start in permanent jobs.temporary jobs, fixed term contracts, individual unobserved heterogeneity, job-specific effects.
Impact and Compression-After-Impact Performance of a Thin Z-Pinned Composite Laminate
Impact and compression-after-impact (CAI) tests were carried out on [02/ ± 45]s carbon/epoxy samples to characterize the effect of z-pinning on the delamination resistance and damage tolerance properties of the laminate. Unpinned and z-pinned samples were subjected to impacts between 2 and 36 J to produce damage conditions that extend from barely visible impact damage (BVID) to complete penetration. The damage induced by impact and the damage modes leading to ultimate CAI failure were examined by Xradiography and by direct observations of the sample faces during CAI loading. The analyses indicate that the role of z-pins on the impact and CAI response of the laminate is dependent on the size and features of
the damage. Z-pins do not modify the structural response to impact of the laminate, but they are effective in reducing the extent of damage for impact energies above a threshold value. Z-pinning is also effective in improving the CAI strength of the laminate for impact energies above this threshold value, even though it degrades the residual compressive strength for lower impact energies. Reductions in impact delamination size of up to 50% and improvements in CAI strength of about 20% were achieved by z-pinning for highenergy impacts. The mechanisms by which the z-pins affect the CAI response of the samples are illustrated and examined in detail for different impact damage severities
Structure and electronic properties of the quasi-one-dimensional BaâCoâââZnâSâ series
This work focuses on the structure and physical properties of the solid solution BaâCoâââZnâSâ (0 †x †1), a family of quasi-one-dimensional sulfides with end members BaâCoSâ and BaâZnSâ. The structure of selected compounds with increasing ZnÂČâș content has been analysed using, neutron diffraction, TEM and EXAFS and the physical properties via magnetic susceptibility and resistivity measurements. The progressive substitution of the non-magnetic ZnÂČâș cation for CoÂČâș rapidly destroys the antiferromagnetic transition present at 46 K in the quasi one-dimensional BaâCoSâ, leading to paramagnetic behaviour down to the lowest investigated temperature (5K) for compounds with x > 0.25. For compounds with x â„ 0.4, a pure CW regime is recovered around 300 K, yielding effective moments consistent with the g factor of the tetrahedrally coordinated CoÂČâș previously determined for BaâCoSâ. The ZnÂČâș/CoÂČâș substitution also removes the metallic-like behaviour of BaâCoSâ causing an increase in the value of the resistivity with all the BaâCoâââZnâSâ compounds showing semiconducting behaviour. The negative magnetoresistance of BaâCoSâ is improved by the ZnÂČâș/CoÂČâș substitution, with values of â 6% for BaâCoâ.ââ
Znâ.ââ
Sâ, â 9% for BaâCoâ.â
Znâ.â
Sâ and â 8% for BaâCoâ.ââ
Znâ.ââ
Sâ. However, there does not seem to be a correlation between the values of the resistivity and the magnetoresistance and the content of ZnÂČâș, leading to the hypothesis that transport properties may be linked more closely to extrinsic properties
Numerical analysis of energy recovery system for turbocharged internal combustion engines via a parallel compounding turbine
Increasing energy efficiency requirements mandatory ask for optimizing energy utilization in many devices, which include internal combustion engines. One of the most investigated subjects is the energy recovery from the exhaust, such as turbo-compound systems, which usually consist in a secondary turbine located afterward the turbocharger. Here an alternative arrangement is proposed and analysed via a numerical model. The recovery turbine works in parallel to the main turbine and uses the gasses which would be otherwise wasted through the waste-gate valve, once the set-point boost pressure is reached. The reference case analysed is a 12.4L turbocharged diesel engine, commonly used in marine, road and light railroad applications, with a nominal power of 380kW. The results showed that an overall 8% of power can be gained, without nor increasing the fuel mass flow rate, neither requiring significant modifications to the baseline engine. Moreover, in the case of the recovery system failure, the operation of the engine is not affected, thus resulting in no engine availability reduction. This work also shows a feasible way to convert the mechanical energy delivered by the recovery turbine into electrical energy, by making use of a high-speed electrical generator
Effect of parent concrete on the performance of recycled aggregate concrete
Recycling concrete construction waste is a promising way towards sustainable construction. Indeed, replacing natural aggregates with recycled aggregates obtained from concrete waste lowers the environmental impact of concrete constructions and improves natural resource conservation. This paper reports on an experimental study on mechanical and durability properties of concretes casted with recycled aggregates obtained from two different parent concretes, belonging to two structural elements of the old Cagliari stadium. The effects of parent concretes on coarse recycled aggregates and on new structural concretes produced with different replacement percentages of these recycled aggregates are investigated. Mechanical properties (compressive strength, modulus of elasticity, and splitting tensile strength) and durability properties (water absorption, freeze thaw, and chloride penetration resistance) are experimentally evaluated and analyzed as fundamental features to assess structural concrete behavior. The results show that the mechanical performance of recycled concrete is not related to the parent concrete characteristics. Furthermore, the resistance to pressured water penetration is not reduced by the presence of recycled aggregates, and instead, it happens for the chloride penetration resistance. The resistance to frostâthawing seems not related to the recycled aggregates replacement percentage, while an influence of the parent concrete has been assessed
Consistency and diversity of spike dynamics in the neurons of bed nucleus of Stria Terminalis of the rat: a dynamic clamp study
Neurons display a high degree of variability and diversity in the expression and regulation of their voltage-dependent ionic channels. Under low level of synaptic background a number of physiologically distinct cell types can be identified in most brain areas that display different responses to standard forms of intracellular current stimulation. Nevertheless, it is not well understood how biophysically different neurons process synaptic inputs in natural conditions, i.e., when experiencing intense synaptic bombardment in vivo. While distinct cell types might process synaptic inputs into different patterns of action potentials representing specific "motifs'' of network activity, standard methods of electrophysiology are not well suited to resolve such questions. In the current paper we performed dynamic clamp experiments with simulated synaptic inputs that were presented to three types of neurons in the juxtacapsular bed nucleus of stria terminalis (jcBNST) of the rat. Our analysis on the temporal structure of firing showed that the three types of jcBNST neurons did not produce qualitatively different spike responses under identical patterns of input. However, we observed consistent, cell type dependent variations in the fine structure of firing, at the level of single spikes. At the millisecond resolution structure of firing we found high degree of diversity across the entire spectrum of neurons irrespective of their type. Additionally, we identified a new cell type with intrinsic oscillatory properties that produced a rhythmic and regular firing under synaptic stimulation that distinguishes it from the previously described jcBNST cell types. Our findings suggest a sophisticated, cell type dependent regulation of spike dynamics of neurons when experiencing a complex synaptic background. The high degree of their dynamical diversity has implications to their cooperative dynamics and synchronization
Incidenza della sclerosi multipla in Toscana: uno studio basato su dati amministrativi
INTRODUZIONE
LâItalia Ăš unâarea ad elevato rischio di sclerosi multipla (SM) con una prevalenza stimata di 75.000 casi e unâincidenza di 2.000 casi annui. Gli ultimi dati pubblicati sullâincidenza sono 5,5 casi/105 a Padova (2000-09), 6,6 a Genova (1998-2007) e 9,7 in Sardegna (2003-07). In Toscana Ăš presente un registro regionale della SM ma, ad oggi, non Ăš rappresentativo dellâintera popolazione. Una possibile alternativa per studiare lâepidemiologia Ăš attraverso i dati amministrativi. Questi, infatti, coprono lâintera popolazione residente e vengono raccolti di routine in un modo standardizzato ai fini della gestione del servizio sanitario.
Il nostro scopo Ăš calcolare lâincidenza della SM in Toscana utilizzando dati amministrativi.
METODI
Per il calcolo dellâincidenza abbiamo creato il seguente algoritmo: ospedalizzazione in reparto per acuti e con diagnosi primaria di SM, esenzione attiva per SM, e prescrizione di farmaci specifici. I casi incidenti sono stati identificati come quei casi catturati dallâalgoritmo non tracciati in precedenza nei flussi amministrativi, e la data della prima traccia Ăš stata considerata quale data di diagnosi della SM. Da questa coorte di soggetti abbiamo selezionato i pazienti con unâetà †55 anni, residenti in Toscana al momento della diagnosi e presenti in anagrafe da almeno 10 anni (o nati in Toscana se etĂ <10). Abbiamo calcolato i tassi grezzi e standardizzati e gli intervalli di confidenza (IC) al 95% per gli anni 2011-2015.
RISULTATI
Abbiamo identificato, negli anni analizzati, 1.056 nuovi casi con unâincidenza che varia da 5,04/105 nel 2011 a 6,02 casi/105nel 2015 (Tab 1). Nelle donne lâincidenza Ăš circa due volte piĂč alta rispetto agli uomini con un range che va da 6,48 a 7,96/105 nelle donne, e da 3,49 a 3,93/105 negli uomini.
CONCLUSIONI
Lâincidenza calcolata risulta elevata, soprattutto nelle donne, ma comunque in linea ai dati pubblicati in altre Regioni, al di lĂ dei bias metodologici legati allâuso di dati amministrativi
Measurement of tissue oxygenation in isolated rat hearts using near infrared spectroscopy
New techniques involving Near Infrared Spectroscopy (NIRS) and imaging are rapidly evolving for a large number of new clinical applications. These techniques, based upon nearinfrared light transmission through biological tissue, aim to monitor the hemoglobin and myoglobin concentration changes due to particular physiological state. Clinical applications regard, for instance, the monitoring of muscles and cerebral oxygenation, functional brain activation studies and heart perfusion research. Recently, some works presented tissue oxygenation studies in beating or arrested isolated porcine hearts. In our work we present the design and realization of a dedicated NIRS system for the myocardial perfusion analysis of isolated, saline solution perfused beating rat hearts; in this case the absence of blood allows for unambiguous measurement of tissue myoglobin oxygenation. The presented prototype is portable, low cost, battery operated and permits the measurement of both oxy and deoxy myoglobin concentration changes during imposed regional or global ischemia and reperfusion
The front end electronics for the drift chamber readout in MEG experiment upgrade
Front-end electronics plays an essential role in drift chambers for time resolution and, therefore, spatial resolution. The use of cluster timing techniques, by measuring the arriving times of all the individual ionization clusters after the first one, may enable to reach resolutions even below 100 ÎŒm in the measurement of the impact parameter. A high performance front-end electronics, characterized by low distortion, low noise and a wide bandwidth has been developed with the purpose to implement cluster timing techniques in the new drift chamber for the upgrade of the MEG experiment at Paul Sherrer Institut (CH)
Commissioning of the MEG II tracker system
The MEG experiment at the Paul Scherrer Institut (PSI) represents the state
of the art in the search for the charged Lepton Flavour Violating (cLFV) decay. With the phase 1, MEG set the new world best
upper limit on the \mbox{BR}(\mu^+ \rightarrow e^+ \gamma) < 4.2 \times
10^{-13} (90% C.L.). With the phase 2, MEG II, the experiment aims at reaching
a sensitivity enhancement of about one order of magnitude compared to the
previous MEG result. The new Cylindrical Drift CHamber (CDCH) is a key detector
for MEG II. CDCH is a low-mass single volume detector with high granularity: 9
layers of 192 drift cells, few mm wide, defined by wires in a
stereo configuration for longitudinal hit localization. The filling gas mixture
is Helium:Isobutane (90:10). The total radiation length is
\mbox{X}_0, thus minimizing the Multiple Coulomb Scattering (MCS)
contribution and allowing for a single-hit resolution m and an
angular and momentum resolutions of 6 mrad and 90 keV/c respectively. This
article presents the CDCH commissioning activities at PSI after the wiring
phase at INFN Lecce and the assembly phase at INFN Pisa. The endcaps
preparation, HV tests and conditioning of the chamber are described, aiming at
reaching the final stable working point. The integration into the MEG II
experimental apparatus is described, in view of the first data taking with
cosmic rays and beam during the 2018 and 2019 engineering runs. The
first gas gain results are also shown. A full engineering run with all the
upgraded detectors and the complete DAQ electronics is expected to start in
2020, followed by three years of physics data taking.Comment: 10 pages, 12 figures, 1 table, proceeding at INSTR'20 conference,
accepted for publication in JINS
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