3,133 research outputs found
Factors affecting wood, energy grass and straw pellet durability â A review
Pellets produced from wood, energy grasses and straw present a higher energy density feedstock than wood chips or bales, and therefore reduce the costs of handling, transport and storage throughout the supply chain. European specifications provide limits to the proportion of fines (particles less than 3.15 mm) allowed in pellets, which refers to the durability of the pellets. Fines have implications for health and safety in supply chains, and cause issues with slag formation in combustion systems. This paper reviews the factors affecting biomass pellet durability. The industrial trade for wood pellets has expanded greatly over the last decade and involves the international trade of tens of million tonnes annually. Due to increasing demands for pellets, there has been growing interest in utilising more varied biomass types. The aim of this review is to examine feedstock qualities and pelleting conditions that produce durable pellets. Pellet durability can be affected by the feedstock characteristics, the moisture content or size reduction during pre-processing, and by pelleting conditions, including the use of binders, feedstock mixes, temperatures or die pressures. Post-production conditions can also affect durability, such as the storage conditions and handling frequency, therefore an understanding of all the factors affecting durability throughout the supply chain is needed in order to prioritise where advances can be made
Nuclear Dynamics During Landau-Zener Singlet-Triplet Transitions in Double Quantum Dots
We consider nuclear spin dynamics in a two-electron double dot system near
the intersection of the electron spin singlet and the lower energy
component of the spin triplet. The electron spin interacts with nuclear
spins and is influenced by the spin-orbit coupling. Our approach is based on a
quantum description of the electron spin in combination with the coherent
semiclassical dynamics of nuclear spins. We consider single and double
Landau-Zener passages across the - anticrossings. For linear sweeps,
the electron dynamics is expressed in terms of parabolic cylinder functions.
The dynamical nuclear polarization is described by two complex conjugate
functions related to the integrals of the products of the
singlet and triplet amplitudes
along the sweep. The real part of is related to the
- spin-transition probability, accumulates in the vicinity of the
anticrossing, and for long linear passages coincides with the Landau-Zener
probability , where is the Landau-Zener
parameter. The imaginary part of is specific for the nuclear
spin dynamics, accumulates during the whole sweep, and for
is typically an order of magnitude larger than . has a profound effect
on the nuclear spin dynamics, by (i) causing intensive shake-up processes among
the nuclear spins and (ii) producing a high nuclear spin generation rate when
the hyperfine and spin-orbit interactions are comparable in magnitude. We find
analytical expressions for the back-action of the nuclear reservoir represented
via the change in the Overhauser fields the electron subsystem experiences.Comment: 19 pages, 5 figure
The role of UK alcohol and drug (AOD) nurses in a changing workforce
Background: This paper presents the findings from an exploratory study on alcohol and other drugs (AOD) nursesâ views on current career opportunities and challenges and on how their role has been affected by clinical and structural changes in service delivery.
Methods: The paper is based on qualitative interviews with a purposive sample of twelve AOD nurses in the UK. A narrative approach to interviewing aimed to encourage emergence of new insights and suggest theories for future examination. Interview domains were informed by the research teamâs knowledge of AOD nursing and by themes from published literature. Interviews were recorded, transcribed, and coded and a reflexive thematic analysis was conducted.
Results: Key themes emerging focused on the growth, advantages, and challenges of non-medical prescribing (NMP), and the impact on AOD nursing of changes in workforce structures and environments. The findings indicate considerable doubts about career opportunities for nurses in AOD services although NMP may offer some limited routes to career advancement.
Conclusions: Some long-standing issues around the identity and professional status of AOD nurses persist and current clinical and structural changes have created a âliminal spaceâ within which the nursing role and AOD nurse identity are disrupted and in transition
How well does Miscanthus ensile for use in an anaerobic digestion plant?
This study examined the ability for early-harvested Miscanthus (Miscanthus x giganteus and Miscanthus sacchariflorus) to be stored in silage for later use in anaerobic digestion. Two silage additives favouring a homo and hetero-fermentation pathway were examined. The results show that silage additives are necessary to effectively ensile Miscanthus, otherwise untreated Miscanthus grasses incurred dry matter losses of 4% during three months' storage. The silage additives improved the lactic and acetic acid production in the Miscanthus silages however did not have any effect on the biogas yield. On a âper tonne volatile solidsâ-basis, Miscanthus produces half the biogas yield of maize. The outlook for the use of Miscanthus AD therefore depends on the yield when harvested in autumn. A minimum yield of 19â26.5 t DM/ha is needed for Miscanthus to match the biogas production from a similar area of maize yielding 10â14 t DM/ha
Edgeworth Expansion of the Largest Eigenvalue Distribution Function of GUE Revisited
We derive expansions of the resolvent
Rn(x;y;t)=(Qn(x;t)Pn(y;t)-Qn(y;t)Pn(x;t))/(x-y) of the Hermite kernel Kn at the
edge of the spectrum of the finite n Gaussian Unitary Ensemble (GUEn) and the
finite n expansion of Qn(x;t) and Pn(x;t). Using these large n expansions, we
give another proof of the derivation of an Edgeworth type theorem for the
largest eigenvalue distribution function of GUEn. We conclude with a brief
discussion on the derivation of the probability distribution function of the
corresponding largest eigenvalue in the Gaussian Orthogonal Ensemble (GOEn) and
Gaussian Symplectic Ensembles (GSEn)
Instability of coherent states of a real scalar field
We investigate stability of both localized time-periodic coherent states
(pulsons) and uniformly distributed coherent states (oscillating condensate) of
a real scalar field satisfying the Klein-Gordon equation with a logarithmic
nonlinearity. The linear analysis of time-dependent parts of perturbations
leads to the Hill equation with a singular coefficient. To evaluate the
characteristic exponent we extend the Lindemann-Stieltjes method, usually
applied to the Mathieu and Lame equations, to the case that the periodic
coefficient in the general Hill equation is an unbounded function of time. As a
result, we derive the formula for the characteristic exponent and calculate the
stability-instability chart. Then we analyze the spatial structure of the
perturbations. Using these results we show that the pulsons of any amplitudes,
remaining well-localized objects, lose their coherence with time. This means
that, strictly speaking, all pulsons of the model considered are unstable.
Nevertheless, for the nodeless pulsons the rate of the coherence breaking in
narrow ranges of amplitudes is found to be very small, so that such pulsons can
be long-lived. Further, we use the obtaned stability-instability chart to
examine the Affleck-Dine type condensate. We conclude the oscillating
condensate can decay into an ensemble of the nodeless pulsons.Comment: 11 pages, 8 figures, submitted to Physical Review
Collapse-and-revival dynamics of strongly laser-driven electrons
The relativistic quantum dynamics of an electron in an intense single-mode
quantized electromagnetic field is investigated with special emphasis on the
spin degree of freedom. In addition to fast spin oscillations at the laser
frequency, a second time scale is identified due to the intensity dependent
emissions and absorptions of field quanta. In analogy to the well-known
phenomenon in atoms at moderate laser intensity, we put forward the conditions
of collapses and revivals for the spin evolution in laser-driven electrons
starting at feasible W/cm.Comment: 18 pages, 4 figure
Infinite spin particles
We show that Wigner's infinite spin particle classically is described by a
reparametrization invariant higher order geometrical Lagrangian. The model
exhibit unconventional features like tachyonic behaviour and momenta
proportional to light-like accelerations. A simple higher order superversion
for half-odd integer particles is also derived. Interaction with external
vector fields and curved spacetimes are analyzed with negative results except
for (anti)de Sitter spacetimes. We quantize the free theories covariantly and
show that the resulting wave functions are fields containing arbitrary large
spins. Closely related infinite spin particle models are also analyzed.Comment: 43 pages, Late
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