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Biomedical subjects

L Frank

Publications and source records attributed to L Frank.

178 records · Page 10Linked to original sources
PubMedDate not supplied

Scanning electron microscopy of nonconductive specimens at critical energies in a cathode lens system.

A method for scanning electron microscopy imaging of nonconductive specimens, based on measurement and utilisation of a critical energy, is described in detail together with examples of its application. The critical energy, at which the total electron yield curve crosses the unit level, is estimated on the basis of measurement of the image signal development from the beginning of irradiation. This approach, concentrated onto the detected signal as the only quantity crucial for the given purpose of acquiring a noncharged micrograph, evades consequences of any changes in an irradiated specimen that influence the total electron yield curve and possibly also the critical energy value. Implementation of the automated method, realised using a cathode lens-equipped scanning electron microsope (SEM), enables one to establish a mean rate of charging over the field of view and its dependence on the electron landing energy. This dependence enables one to determine the energy of a minimum damage of the image of the given field of view. Factors influencing reliability and applicability of the method are discussed and examples of noncharged micrographs of specimens from both life and material science fields are presented.

Actinomycetales↗
PubMedDate not supplied

Specimen charging and detection of signal from non-conductors in a cathode lens-equipped scanning electron microscope.

This paper concerns the problems connected with the observation of a nonconductive specimen in a scanning electron microscope (SEM) when incident electrons create a surface charge and a corresponding electric field. The special configuration of the cathode lens enables one to control the landing energy of primary electrons via the specimen bias. In the cathode lens, the accelerating electric field at the surface of the specimen combines itself with that of the surface charge in influencing the trajectories of the signal electrons and hence the detected signal level and the possible recapturing of slow secondaries. Recaptured electrons reduce the ultimate positive surface potential, which arises when working below the higher critical energy of electron impact. Computer simulations of electron trajectories were performed for the typical cathode lens configuration and for a model specimen characterized by emission yields similar to those for glass. The simulations brought an extensive set of data about the trajectories of both secondary and backscattered electrons. Furthermore, the data were processed in order to assess the charge balance between the emitted and recaptured electrons as well as the collection efficiency of the detector. The results include values of the ultimate positive surface potential and the detected signal level, both in dependence on the initial energy of the electron impact and the size of the field of view. Finally, the method for the determination of critical energy is reevaluated. This is based on the measurement of the time dependence of the detected signal.

Journal Article↗
PubMedDate not supplied

Corrections of magnification and focusing in a cathode lens-equipped scanning electron microscope.

One of the well-proven and efficient methods of obtaining a very low-energy impact of primary electrons in the scanning electron microscope is to introduce a retarding field element below the pole piece of the objective lens (OL). It is advantageous to use the specimen alone as the negatively biased electrode (i.e., cathode of the cathode lens). The optical power of the cathode lens modifies some of the standard parameters of the image formation such as relation of working distance to OL excitation or magnification to the scanning coils current, the impact angle of primary electrons, and so forth. In computer-controlled electron microscopes these parameters, particularly with regard to focusing and magnification, can be corrected automatically. Derivation of algorithms for such corrections and their experimental verifications are presented in this paper. Furthermore, a more accurate analytical expression for the focal length of an aperture lens is derived.

Journal Article↗
PubMedDate not supplied

Prisons and public health: emerging issues in HIV treatment adherence.

Correctional facilities in the United States are faced with challenges in providing appropriate and timely HIV treatment to incarcerated HIV-infected inmates. Prison and jails, due to their structure, operation, and staff, may present many barriers to HIV treatment and adherence to complicated and expensive HIV treatment regimens. Changes and modifications of prison health care delivery are required to accommodate the needs of HIV-infected inmates. Approaches to improving correctional HIV care and treatment include training health care personnel, prevention education for inmates, increasing access to voluntary HIV testing, comprehensive treatment planning, and continuity of care. Policy changes for correctional systems include adopting current HIV care standards and immediate evaluation for and access to HIV treatment upon entry into the institution. These changes can have a significant impact on the quality of care for inmates, ultimately improving their quality of life and reducing the morbidity and mortality of HIV disease for incarcerated populations.

Allied Health Personnel↗
PubMedDate not supplied

Intertarsal ligaments: high resolution MRI and anatomic correlation.

High resolution MRI was performed on four cadaveric foot specimens of human feet to demonstrate the ligaments of the tarsal joints. Spin echo T1 images were obtained using a local gradient coil that produces 6 G/cm and 100 A in all three axes. The best views for each of the individual ligaments were determined. High resolution MRI potentially can demonstrate most of the intertarsal ligaments.

Aged↗
PubMedDate not supplied

Differential effect of NMDA and AMPA receptor blockade on protein synthesis in the rat infarct borderzone.

We investigated whether the known neuroprotective effects of two selective glutamate receptor antagonists, the NMDA antagonist MK-801 and the AMPA antagonist NBQX, are reflected in the regional cerebral protein synthesis rates (CPSR) in rats with middle cerebral artery occlusion (MCAO). Rats treated with either saline, MK-801 (5 mg/kg i.p.) or NBQX (30 mg/kg i.p. x 3) were subjected to permanent MCAO. Regional CPSR and volumes of gray matter structures displaying normal CPSR were measured in coronal cryosections of the brain by quantitative autoradiography following an i.v. bolus injection of 35S-labelled L-methionine 2 h after occlusion. MCAO completely inhibited protein synthesis in the lateral part of striatum and part of the adjacent frontoparietal cortex corresponding to the ischemic focus. Surrounding this, a metabolic penumbra with approximately 50% reductions in CPSR was present. Treatment with MK-801 significantly increased the volume of tissue with normal CPSR in the ischemic hemisphere compared to controls, whereas this was not seen with NBQX treatment. The results suggest that MK-801 and NBQX have different effects on peri-infarct protein synthesis after MCAO. Since both compounds reduce infarct size, it is questionable that acute inhibition of protein synthesis in focal ischemia is of significant importance to the final outcome of a stroke lesion.

Animals↗
PubMedDate not supplied

Dramatic changes in care: the experience of one psychiatric hospital.

Recent and dramatic changes in this country's mental healthcare service are widely documented. To assess the extent and timing of those changes at one private psychiatric hospital, the authors examined length of stay, number of admissions, and patient age for general trends between 1980 and 1990 and more closely examined trends between July 1990 and December 1991. We related our findings to data for other private psychiatric hospitals and compared them with data from psychiatric units in general hospitals. The results are discussed in terms of changes in insurance coverage, changing utilization by different age groups, and a national shift from inpatient to outpatient care.

Adult↗
PubMedDate not supplied

[The role of chronic renal insufficiency in the prognosis of surgical interventions in subrenal abdominal aortic aneurysm].

Chronic renal insufficiency is one of the most important factors governing the immediate and long-term outcome after aneurysm repair. A total of 484 patients with abdominal aortic aneurysm (A.A.A.) have undergone elective surgical treatment in our Institution during the last 5 years. Of these, we selected 60 patients; 30 with a normal serum creatinine concentration and 30 with preoperative renal insufficiency (serum creatinine concentration greater than 2 mg/dl). In this second group, 23 patients (76.6%) were affected by slight or median renal insufficiency, 5 patients (16.6%) were affected by severe renal insufficiency (creatinine concentration greater than 4.5 mg/dl), and 2 patients (6.6%) had complete renal failure with dialytic treatment from 1.5 and 2 years respectively. We analyzed postoperative renal function in all 60 patients. In the first group, only 6 patients (20%) showed a transient renal insufficiency, without mortality and morbidity. In the second group, postoperative complications and mortality tended to occur more frequently in patients with a severe renal insufficiency than in patients with slight or median insufficiency or complete renal failure. The present data suggest that dialytic treatment might be necessary in patients with severe renal insufficiency before aneurysm repair.

Aortic Aneurysm, Abdominal↗