The prevalence of preferential nasal breathing in adults

The prevalence of preferential nasal breathing was studied in an awake adult population. One hundred and ninety-four people consented to gentle manual compression of the nostrils. They were advised to 'breathe in and out', but no further information regarding breathing was given to avoid influencing the patient. One hundred and eighty patients (92.8%) commenced immediate regular relaxed breathing. Fourteen patients (7.2%) had difficulty with oral breathing which ranged from irregular mouth breathing associated with distress to no spontaneous respiration. The prevalence of preferential nasal breathing was strongly associated with increasing age (chi 2 for trend, P = 0.007). In addition, a weakly significant association was demonstrated between a history of asthma and this phenomenon (P = 0.047). These findings suggest a tendency for the elderly person to revert to the infant pattern of obligate nasal breathing. Physicians should be aware of this possibility in the elderly patient, especially prior to any procedure which may induce nasal obstruction.     

A noise resistant synchronization scheme for HDTV images

A method that increases the error resistance of the HDTV system and offers graceful picture degradation in the presence of bit errors, is presented. Due to the nature of the presently proposed compression schemes for HDTV systems, an error in a data bit does not only affect the block the bit belongs to, but unfortunately the effects of this error may perpetuate to the following blocks. This is because a bit error may cause loss of synchronization between the data bits and the picture blocks they represent. Our method restricts the effects of a bit error to a picture block whose size is significantly smaller than those used by the HDTV systems. We achieve synchronization by transmitting a header-word for each such synchronization block. Each header-word contains the number of data bits representing the compressed block. This header-word is protected by two levels of FEC code. To decrease the number of extra bits needed by the header-words, two different synchronization block sizes are used, a relatively small block size for the reference frames and a larger size for the inter-frames. The resulting method improves the quality of the picture in the presence of errors and defers the SNR at which the HDTV picture suddenly deteriorates by 2.5 to 3 dB. It also allows operation at higher order modulation transmission schemes, e.g., 32-QAM instead of 16-QAM, without the requirement of increased signal power     

A Method for Measuring Pulsed Amplifier Noise Using a Spectrum Analyzer

Measuring the noise generated by a pulsed RF amplifier is not a simple task [1]. One method of making this measurement converts the RF pulse to video with a phase detector and uses a spectrum analyzer to measure the noise between the lines of the pulse spectrum. The measurement includes the combined effects of timing jitter, power-supply modulation, and amplifier noise. An alternate method, described in this note, requires less test equipment by using an RF spectrum analyzer to measure the noise at a point outside the pulse spectrum. This measurement responds only to amplifier noise and is valid if the noise density is the same both inside and outside the pulse spectrum. Since this situation tends to be true of broad-band amplifiers such as TWT's and CFA's, the second method is preferable because of its relative simplicity. This note describes the procedure for measuring pulsed amplifier noise using an RF spectrum analyzer. The test setup and measurement procedure are described, as well as the conversion of the measured spectral-density ratio to an equivalent CW signal-to-noise ratio.     

A Device to Provide Respiratory-Mechanical Unloading

A commercially available and widely used servo-controlled ventilator has been modified to provide controlled inspiratory resistive unloading of the human respiratory system. This is achieved by establishing a positive mouth pressure throughout inspiration in a constant proportion to instantaneous flow, i.e., the ratio of mouth pressure to flow, which defines the "assistance," remaining constant. The performance of this device has been evaluated in four healthy subjects during steady-state, constant-load cycling (20-120 W). It is demonstrated that i) the device can successfully implement controlled degrees of inspiratory assistance on a breath-to-breath basis; ii) the assistance can be sustained over a substantial range of ventilatory drive (i.e., for ventilations up to some 30 1/min) and to an extent which approaches a 100 percent reduction of the normal respiratory resistance. This device should prove useful in experimental and clinical investigations of the respiratory responses to resistive unloading of the respiratory system.     

Fibular shortening in poliomyelitis

We have determined the nucleotide and encoded amino acid sequences of the capsid, membrane precursor, membrane, envelope, and nonstructural NS1 protein genes of a dengue-2 virus (D2-04) isolated from a patient in Hainan, China. The sequenced region contains a gene organization similar to that of other flaviviruses. The overall amino acid sequence similarity between D2-04 and other dengue-2 viruses is greater than 92%, whereas that between D2-04 and members of the other dengue serotypes is about 65%.     

Experimental evidence for mode shape influence on acceleration-induced frequency shifts in quartz resonators

Experimental results are presented to support the hypothesis that the shape and location of the active region of vibration in a thickness shear mode quartz resonator are the dominant factors in determining the acceleration sensitivity of the resonator. The shape and location of the mode in a real world resonator vary sufficiently from unit to unit (due to material and processing variations) that all other considerations are overwhelmed. It is shown experimentally that the mode shape and/or location can be trimmed with energy trapping by judicious addition or subtraction of mass to produce resonators with improved acceleration sensitivity.     

The yield behaviour of amorphous polyethylene terephthalate: An activated rate theory approach

Yield-stress measurements on amorphous polyethylene terephthalate film are presented covering five decades of strain rate at temperatures from just below the glass transition ( 60° C) to –160° C. The data were obtained by combining measurements from a conventional Instron machine with data from a high-speed tensile tester capable of applying strain rates of up to 50 sec^–1. Five different failure modes have been identified over this extensive range of test conditions. All data from tests which show a clear yield point can be described accurately by an extension of the Ree Eyring approach to include two processes. The process which is only important at low temperatures correlates well with the-process observed in dynamic mechanical experiments.