16,622 research outputs found
The testing of gel fuels, and their comparison to alternative cooking fuels
A range of gel fuels was tested in a range of appliances designed for the fuels. The tests comprised the determination of the efficiency of the fuel/appliance combination when boiling water at full and, where possible, minimum power; and the measurement of CO, CO2 and unburned hydrocarbons collected in a hood at the burner level in normal operation. The tests were repeated with paraffin-fuelled appliances, LP gas appliances and an electric stove. In the majority of cases it was found that the gel fuels did not meet an emission standard of a CO:CO2 ratio of <0.02, and that they gave off excessive unburned hydrocarbons. It was suspected that this had to do with the mixing of the fuel vapour with air, because tests with pure ethanol in various appliances gave similar results. Tests in which appliances were modified to improve the air/fuel mixing showed that the hypothesis was valid. A subsidiary finding of the tests was that some gel fuels had excessive water, and that in these cases the condensation of the water vapour on the base of a cooking pot was so extensive that it could extinguish the flame. This leads to a recommendation that a standard for gel fuels be established. A comparison of the cost of cooking a standard meal suggests that gel fuels are unlikely to meet users needs even if improved appliances can be developed
The value of psychological flexibility: Examining psychological mechanisms underpinning a cognitive behavioural therapy intervention for burnout
Little is known of the mechanisms by which interventions for burnout work. Employees of a UK government department were randomly assigned to either a worksite group-based CBT intervention called Acceptance and Commitment Therapy (ACT; n=43), which aimed to increase participants' psychological flexibility, or a waiting list control group (n=57). The ACT group received three half-day sessions of training spread over two and a half months. Data were collected at baseline (T1), at the beginning of the second (T2) and third (T3) workshops, and at six months' follow up (T4). Consistent with ACT theory, analyses revealed that, in comparison to the control group, a significant increase in psychological flexibility from T2 to T3 in the ACT group mediated the subsequent T2 to T4 decrease in emotional exhaustion in that group. Consistent with a theory of emotional burnout development, this significant decrease in emotional exhaustion from T2 to T4 in the ACT group appeared to prevent the significant T3 to T4 increase in depersonalization seen in the control group. Strain also decreased from T2 to T3 in the ACT group only, but no mediator of that improvement was identified. Implications for theory and practice in the fields of ACT and emotional burnout are discussed
Mindfulness and meditation in the workplace: An acceptance and commitment therapy approach
There is a wide-range and growing body of evidence that mental health and behavioural effectiveness are influenced more by how people interact with their thoughts and feelings than by their form (e.g., how negative they are) or frequency. Research has demonstrated this key finding in a wide-range of areas. For example, in chronic pain, psychosocial disability is predicted more by the experiential avoidance of pain than by the degree of pain (McCracken, 1998). A number of therapeutic approaches have been developed that share this key insight: distress tolerance (e.g., Brown, Lejuez, Kahler, & Strong, 2002; Schmidt, Richey, Cromer, & Buckner, 2007), thought suppression (e.g., Wenzlaff & Wegner, 2000), and mindfulness (Baer, 2003). It is also central to a number of the newer contextual cognitive behaviour therapy (CBT) approaches to treatment, such as mindfulness based cognitive therapy (MBCT; Segal, Williams, & Teasdale, 2001), dialectical behaviour therapy (DBT; Linehan, 1993), metacognitive therapy (Wells, 2000), and acceptance and commitment therapy (ACT; Hayes, Strosahl, & Wilson, 1999).
The purpose of this chapter is to describe how ACT conceptualises mindfulness and tries to enhance it in the pursuit of promoting mental health and behavioural effectiveness (e.g., productivity at work). To this end, we discuss ACT’s key construct of psychological flexibility, which involves mindfulness, and how it has led to a somewhat different approach not only to conceptualising mindfulness, but also how we try to enhance it in the workplace. In so doing, we hope to show that whilst formal meditation practice is valued in ACT, it is only one strategy that is used to promote mindfulness, as well as psychological flexibility more generally
Three-dimensional carrier-dynamics simulation of terahertz emission from photoconductive switches
A semi-classical Monte Carlo model for studying three-dimensional carrier
dynamics in photoconductive switches is presented. The model was used to
simulate the process of photoexcitation in GaAs-based photoconductive antennas
illuminated with pulses typical of mode-locked Ti:Sapphire lasers. We analyzed
the power and frequency bandwidth of THz radiation emitted from these devices
as a function of bias voltage, pump pulse duration and pump pulse location. We
show that the mechanisms limiting the THz power emitted from photoconductive
switches fall into two regimes: when illuminated with short duration (<40 fs)
laser pulses the energy distribution of the Gaussian pulses constrains the
emitted power, while for long (>40 fs) pulses, screening is the primary
power-limiting mechanism. A discussion of the dynamics of bias field screening
in the gap region is presented. The emitted terahertz power was found to be
enhanced when the exciting laser pulse was in close proximity to the anode of
the photoconductive emitter, in agreement with experimental results. We show
that this enhancement arises from the electric field distribution within the
emitter combined with a difference in the mobilities of electrons and holes.Comment: 7 pages, 7 figure
Towards Intelligent Databases
This article is a presentation of the objectives and techniques
of deductive databases. The deductive approach to databases aims at extending
with intensional definitions other database paradigms that describe
applications extensionaUy. We first show how constructive specifications can
be expressed with deduction rules, and how normative conditions can be defined
using integrity constraints. We outline the principles of bottom-up and
top-down query answering procedures and present the techniques used for
integrity checking. We then argue that it is often desirable to manage with
a database system not only database applications, but also specifications of
system components. We present such meta-level specifications and discuss
their advantages over conventional approaches
Influence of surface passivation on ultrafast carrier dynamics and terahertz radiation generation in GaAs
The carrier dynamics of photoexcited electrons in the vicinity of the surface
of (NH4)2S-passivated GaAs were studied via terahertz (THz) emission
spectroscopy and optical-pump THz-probe spectroscopy. THz emission spectroscopy
measurements, coupled with Monte Carlo simulations of THz emission, revealed
that the surface electric field of GaAs reverses after passivation. The
conductivity of photoexcited electrons was determined via optical-pump
THz-probe spectroscopy, and was found to double after passivation. These
experiments demonstrate that passivation significantly reduces the surface
state density and surface recombination velocity of GaAs. Finally, we have
demonstrated that passivation leads to an enhancement in the power radiated by
photoconductive switch THz emitters, thereby showing the important influence of
surface chemistry on the performance of ultrafast THz photonic devices.Comment: 4 pages, 3 figures, to appear in Applied Physics Letter
Topological Protection and Quantum Noiseless Subsystems
Encoding and manipulation of quantum information by means of topological
degrees of freedom provides a promising way to achieve natural fault-tolerance
that is built-in at the physical level. We show that this topological approach
to quantum information processing is a particular instance of the notion of
computation in a noiseless quantum subsystem. The latter then provide the most
general conceptual framework for stabilizing quantum information and for
preserving quantum coherence in topological and geometric systems.Comment: 4 Pages LaTeX. Published versio
The Edge of Quantum Chaos
We identify a border between regular and chaotic quantum dynamics. The border
is characterized by a power law decrease in the overlap between a state evolved
under chaotic dynamics and the same state evolved under a slightly perturbed
dynamics. For example, the overlap decay for the quantum kicked top is well
fitted with (with the nonextensive entropic
index and depending on perturbation strength) in the region
preceding the emergence of quantum interference effects. This region
corresponds to the edge of chaos for the classical map from which the quantum
chaotic dynamics is derived.Comment: 4 pages, 4 figures, revised version in press PR
A dynamic rating curve approach to indirect discharge measurement
Abstract. The operational measurement of discharge in medium and large rivers is mostly based on indirect approaches by converting water stages into discharge on the basis of steady-flow rating curves. Unfortunately, under unsteady flow conditions, this approach does not guarantee accurate estimation of the discharge due, on the one hand, to the underlying steady state assumptions and, on the other hand, to the required extrapolation of the rating curve beyond the range of actual measurements used for its derivation. Historically, several formulae were proposed to correct the steady-state discharge value and to approximate the unsteady-flow stage-discharge relationship. In the majority of these methods, the correction is made on the basis of water level measurements taken at a single cross section where a steady state rating curve is available, while other methods explicitly account for the water surface slope using stage measurements in two reference sections. However, most of the formulae available in literature are either over-simplified or based on approximations that prevent their generalisation. Moreover they have been rarely tested on cases where their use becomes essential, namely under unsteady-flow conditions characterised by wide loop rating curves. In the present work, an original approach, based on simultaneous stage measurements at two adjacent cross sections, is introduced and compared to the approaches described in the literature. The most relevant feature is that the proposed procedure allows for the application of the full dynamic flow equations without restrictive hypotheses. The comparison has been carried out on channels with constant or spatially variable geometry under a wide range of flood wave and river bed slope conditions. The results clearly show the improvement in the discharge estimation and the reduction of estimation errors obtainable using the proposed approach
Quantum Cryptography Approaching the Classical Limit
We consider the security of continuous-variable quantum cryptography as we
approach the classical-limit, i.e., when the unknown preparation noise at the
sender's station becomes significantly noisy or thermal (even by as much as
10,000 times the variance of the vacuum mode). We show that, provided the
channel transmission losses do not exceed 50%, the security of quantum
cryptography is not dependent on the channel transmission, and is therefore,
incredibly robust against significant amounts of excess preparation noise. We
extend these results to consider for the first time quantum cryptography at
wavelengths considerably longer than optical and find that regions of security
still exist all the way down to the microwave.Comment: Letter (4 pages) followed by appendix (4 pages). Updated from
published version with some minor correction
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