375 research outputs found
Dynamics of airflow in a short inhalation
During a rapid inhalation, such as a sniff, the flow in the airways
accelerates and decays quickly. The consequences for flow development and
convective trans- port of an inhaled gas were investigated in a subject
geometry extending from the nose to the bronchi. The progress of flow
transition and the advance of an inhaled non-absorbed gas were determined using
highly resolved simulations of a sniff 0.5 s long, 1 litre per second peak
flow, 364 ml inhaled volume. In the nose, the distribution of airflow evolved
through three phases: (i) an initial transient of about 50 ms, roughly the
filling time for a nasal volume, (ii) quasi-equilibrium over the majority of
the inhalation, and (iii) a terminating phase. Flow transition commenced in the
supraglottic region within 20ms, resulting in large- amplitude fluctuations
persisting throughout the inhalation; in the nose, fluctuations that arose
nearer peak flow were of much reduced intensity and diminished in the flow
decay phase. Measures of gas concentration showed non-uniform build-up and
wash-out of the inhaled gas in the nose. At the carina, the form of the
temporal concentration profile reflected both shear dispersion and airway
filling defects owing to recirculation regions.Comment: 15 page
The Eye in the Neck: Removal of a Sewing Needle from the Posterior Pharyngeal Wall
Foreign body ingestion is a frequent presenting complaint to most emergency departments but the finding of a sewing needle in the posterior pharynx particularly is a rare finding. We report a case of a male patient with a sewing needle lodged in the posterior pharynx despite a history suggestive of chicken bone ingestion, absent clinical features, and negative flexible endoscopic examination. The needle was only identified through cervical spine radiographs. Even subsequent pharyngoscopy, laryngoscopy, and upper oesophagoscopy all proved to be unremarkable with the patient eventually requiring a left neck exploration to remove the needle. The case outlines the importance of simple radiography in suspected foreign body ingestion, even though clinical and endoscopic findings may be unremarkable
The cosmic gravitational wave background in a cyclic universe
Inflation predicts a primordial gravitational wave spectrum that is slightly
``red,'' i.e., nearly scale-invariant with slowly increasing power at longer
wavelengths. In this paper, we compute both the amplitude and spectral form of
the primordial tensor spectrum predicted by cyclic/ekpyrotic models. The
spectrum is blue and exponentially suppressed compared to inflation on long
wavelengths. The strongest observational constraint emerges from the
requirement that the energy density in gravitational waves should not exceed
around 10 per cent of the energy density at the time of nucleosynthesis.Comment: 4 pages, 3 figuer
Quantum Fields in a Big Crunch/Big Bang Spacetime
We consider quantum field theory on a spacetime representing the Big
Crunch/Big Bang transition postulated in the ekpyrotic or cyclic cosmologies.
We show via several independent methods that an essentially unique matching
rule holds connecting the incoming state, in which a single extra dimension
shrinks to zero, to the outgoing state in which it re-expands at the same rate.
For free fields in our construction there is no particle production from the
incoming adiabatic vacuum. When interactions are included the total particle
production for fixed external momentum is finite at tree level. We discuss a
formal correspondence between our construction and quantum field theory on de
Sitter spacetime.Comment: 30 pages, RevTex file, five postscript figure file
Cosmological Perturbations in a Big Crunch/Big Bang Space-time
A prescription is developed for matching general relativistic perturbations
across singularities of the type encountered in the ekpyrotic and cyclic
scenarios i.e. a collision between orbifold planes. We show that there exists a
gauge in which the evolution of perturbations is locally identical to that in a
model space-time (compactified Milne mod Z_2) where the matching of modes
across the singularity can be treated using a prescription previously
introduced by two of us. Using this approach, we show that long wavelength,
scale-invariant, growing-mode perturbations in the incoming state pass through
the collision and become scale-invariant growing-mode perturbations in the
expanding hot big bang phase.Comment: 47 pages, 4 figure
Double Blind Study Investigating the Effect of Different Voice Prostheses on Ease of Swallowing and Residue Post Laryngectomy.
Voice prostheses have been examined for their effect on voice production but there is little datum on their effect on swallow function. This study investigated the difference between six commonly available voice prostheses in terms of swallowing. Laryngectomy patients had up to six voice prostheses placed in a random order over two visits. Swallowing was evaluated for each prosthesis using FEES (Fibreoptic Endoscopic Evaluation of Swallowing). After each prosthesis trial, patients self-evaluated their experience of swallowing. Three independent experts indicated which prosthesis they considered best for swallowing for each patient and judged residue on the voice prosthesis and in the upper esophagus. Raters were blinded to participant details, voice prosthesis type and scores of other raters. On patient self-evaluation, scores were equally distributed across all prostheses for swallowing. Experts most frequently chose the Blom Singer Low pressure and Blom Singer Classic Indwelling voice prostheses as best for swallowing but consensus was poor for most patients. Experts found that the Blom Singer Classic Indwelling and the Provox Vega had least residue on the voice prosthesis on thin liquid (p â€Â 0.001) and soft (p = 0.001), respectively. Experts also found that the Blom Singer Low Pressure had least residue in the upper esophagus on soft consistency (p â€Â 0.001). While self-evaluation by patients did not identify a consistently preferred prosthesis for swallow, many patients expressed personal preferences, suggesting benefits to involving patients in the choice of prosthesis. Some voice prostheses may be associated with lower levels of residue on the prosthesis and upper esophagus with certain consistencies
Conditions for Generating Scale-Invariant Density Perturbations
We analyze the general conditions on the equation of state required for
quantum fluctuations of a scalar field to produce a scale-invariant spectrum of
density perturbations, including models which (in the four dimensional
effective description) bounce from a contracting to an expanding phase. We show
that there are only two robust cases: (inflation) and
(the ekpyrotic/cyclic scenario). All other cases, including the
case considered by some authors, require extreme fine-tuning of initial
conditions and/or the effective potential. For the ekpyrotic/cyclic ()
case, we also analyze the small deviations from scale invariance.Comment: 6 pages, no figure
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