Photosensitized monomerization of 1, 3-dimethyluracil dimers.
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Chemical Phenomena↗
Biomedical subjects
D Elad
Publications and source records attributed to D Elad.
The photosensitized dimerization of thymidine in solution.
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Chemical Phenomena↗
Transport phenomena in the human nasal cavity: a computational model.
Nasal inspiration is important for maintaining the internal milieu of the lung, since ambient air is conditioned to nearly alveolar conditions (body temperature and fully saturated with water vapor) on reaching the nasopharynx. We conducted a two-dimensional computational study of transport phenomena in model transverse cross sections of the nasal cavity of normal and diseased human noses for inspiration under various ambient conditions. The results suggest that during breathing via the normal human nose there is ample time for heat and water exchange to enable equilibration to near intraalveolar conditions. A normal nose can maintain this equilibrium under extreme environments (e.g., hot/humid, cold/dry, cold/humid). The turbinates increase the rate of local heat and moisture transport by narrowing the passageways for air and by induction of laminar swirls downstream of the turbinate wall. However, abnormal blood supply or mucous generation may reduce the rate of heat or moisture flux into the inspired air, and thereby affect the efficacy of the process.
Biological Transport↗
Dynamics of the intrauterine fluid-wall interface.
Intrauterine fluid movements, which are responsible for embryo transport to a successful implantation site at the fundus, may be induced by myometrial contractions. Myometrial contractions in nonpregnant uteri were studied from in vivo measurements of intrauterine pressures with fluid-filled catheters and by visual observations of high-speed replaying of ultrasound images of the uterus. Transvaginal ultrasound (TVUS) images of sagittal cross sections of the nonpregnant uterus were scanned with an intravaginal ultrasound probe. Images at consecutive times (2 s apart) were digitized and processed by employing modern techniques of image processing. The sets of images were compared to evaluate time variation of the fluid-wall interface with respect to amplitude, frequencies, and wavelength of myometrial contractions. Analysis of TVUS images from 11 volunteers during the proliferative phase revealed that myometrial contractions are fairly symmetric and are propagated from the cervix towards the fundus at a frequency of about 0.01-0.09 Hz. The wavelength, amplitude, and velocity of the fluid-wall interface during a typical contractile wave were found to be 10-30 mm, 0.05-0.2 mm, and 0.5-1.9 mm/s, respectively. Additional data acquisition from a large number of normal subjects is needed to build a data base to predict normal characteristics of myometrial contractions in a nonpregnant uterus, in order to better understand their role in the preimplantation process.
Adult↗
A magnetic resonance imaging method of flow by successive excitation of a moving slice.
A new magnetic resonance imaging of flow by a method of successive excitation of a moving slice is presented here. The method, which in general belongs to the class of time-of-flight methods, is based upon selectively changing the frequencies in a sequence of rf pulses in such a way that a selected slice moves through the imaged volume in a preselected direction and velocity, and is repeatedly excited. It is claimed that most of the measured signal is contributed by only those parts of the imaged substance that move with the selected slice. The activation procedure of the flowing spins, which is presented here, enhances the imaging of the flowing matter and reduces the signal from static matter. A specially tailored selective sequence of a rf alpha-pulses has been developed. During this sequence, a set of rephasing 180 degrees selective rf pulses is applied. At the end of this sequence an additional 180 degrees rf pulse is applied to eliminate redundant signals from the static matter in the last activated slice.
Magnetic Resonance Imaging↗
Possible detection of turbulent blood flow using multiparametric encoding gradients in MRI.
Magnetic resonance imaging (MRI) has significant potential as a highly accurate noninvasive flow measurement technique. Presented here is an approach to the imaging of turbulence in the velocity profiles. Recent publications have presented multiparametric encoding gradient methods, which are based on a deterministic rather than a statistical approach to spin motion. Following these methods of building up a general gradient from a basic set of gradients, the effects of turbulence and undetermined moments of motion on the image are discussed. Image blurring due to the nondeterministic behavior of spins (e.g., diffusion, turbulence) is not removed by these techniques, and this fact may be useful in identifying regions of turbulent flow, which are of importance in the clinical observation of cardiac and vascular haemodynamics. Due to its random nature, the elimination of turbulent effects by the use of a deterministic method is bound to fail. On the other hand, regions of turbulent flow may be identified due to signal decrease from those regions, provided one is careful to remove all the causes of nonturbulent signal reduction present due to nonturbulent flow moments. In the multiparametric phase encoding method, gradient amplitude tends to increase with higher moments of motion. The temporal behavior of these gradients is discussed, and it is suggested that the increase in their duration will enhance the encoding of higher motion terms at the expense of imaging time.
Blood Flow Velocity↗