A Novel Band-Reject Element for Pseudoelliptic Bandstop Filters

A novel band-reject element for the design of inline waveguide pseudoelliptic band-reject filters is introduced. The element consists of an offset partial-height post in a rectangular waveguide in which the dominant TE₁₀ mode is propagating. The location of the attenuation pole is primarily determined by the height of the post that generates it. The element allows the implementation of weak, as well as strong coupling coefficients that are encountered in asymmetric band-reject responses with broad stopbands. The coupling strength is controlled by the offset of the post with respect to the center of the main waveguide. The posts are separated by uniform sections of the main waveguide. An equivalent low-pass circuit based on the extracted pole technique is first used in a preliminary design. An improved equivalent low-pass circuit that includes a more accurate equivalent circuit of the band-reject element is then introduced. A synthesis method of the enhanced network is also presented. Filters based on the introduced element are designed, fabricated, and tested. Good agreement between measured and simulated results is achieved     

Near-field optical imaging of unstained bacteria: comparison with normal atomic force and far-field optical microscopy in air and aqueous media

Simultaneous near-field scanning optical and atomic force imaging of bacteria is presented. The bacteria imaged in these studies were unstained. The near-field optical images had excellent signal-to-noise and showed excellent contrast even in these unstained specimens. The images obtained were interpreted in terms of the images that have been obtained by transmission electron microscopy and X-ray imaging. The results show that bacterial near-field optical imaging is going to be a very important tool in the arsenal of the bacteriologist both in terms of understanding the fundamental processes in the life cycle of bacteria with and without cytochemical staining and in terms of clinical diagnostic applications.     

High-breakdown-voltage AlInAs/GaInAs junction-modulated HEMT's(JHEMT's) with regrown ohmic contacts by MOCVD

A technology for increasing both the two-terminal gate-drain breakdown and subsequently the three-terminal-off-state breakdown of AlInAs/GaInAs high-electron-mobility transistors (HEMTs) to record values without substantial impact on other parameters is presented. The breakdown in these structures is dependent on the multiplication of electrons injected from the source (channel current) and the gate (gate leakage) into the channel. In addition, holes are generated by high fields at the drain and are injected back into the gate and source electrodes. These phenomena can be suppressed by increasing the gate barrier height and alleviating the fields at the drain. Both have been achieved by incorporating a p⁺-2DEG junction as the gate that modulates the 2DEG gas and by utilizing selective regrowth of the source and drain regions by MOCVD. The 1-μm-gate-length devices fabricated have two-terminal gate-drain and three-terminal-off-state breakdown voltages of 31 V and 28 V, respectively     

Mycoplasma hyorhinis infection of pigs selectively bred for high and low immune response

Fourier transform infrared microspectroscopy (FTIR) was used to study glasses of pure carbohydrates and in the cytoplasm of desiccation tolerant plant organs. The position of the OH stretching vibration band (vOH) shifted with temperature. Two linear regression lines were observed in vOH against temperature plots. The temperature at the point of intersection between these two lines coincided with the glass transition temperature (Tg), as determined by other methods. The temperature at the intersection point decreased with increasing water content, which further validates that, indeed, Tg was observed. Tg values that were determined for dry glucose, sucrose, maltose, trehalose and raffinose glasses were 27, 57, 91, 108 and 108 degrees C, respectively. The shift of vOH with temperature, the wavenumber-temperature coefficient (WTC), was higher in sugar glasses having higher Tg. This suggests that glasses are more loosely packed when they have higher Tg. For Typha latifolia pollen and dried Craterostigma plantagineum leaves we obtained similar vOH vs. temperature plots as for carbohydrate glasses, indicating that a glass transition was observed. The Tg in dry pollen was ca. 45 degrees C and in dry plant leaves ca. 65 degrees C, with WTC values comparable to those observed in the carbohydrates. The Tg values in these tissues decreased with increasing water contents. Our data suggest that the carbohydrates that are present in the cytoplasm are primary factors contributing to the glassy state. We conclude that FTIR provides new insights in the structure of glasses in carbohydrates and in biological tissues.     

Ion microbeam radiation system

An ion microbeam radiation test system has been built for studying radiation-induced charge collection and single event upsets in advanced semiconductor circuits. With this system, it is possible to direct an ion beam of a diameter as small as 1 μm onto a circuit or test structure with a placement accuracy of 1 μm. The components of the system and its operation are described. Applications are described which demonstrate the capabilities of the system     

Tantalum as a material of construction for the chemical processing industry – A critical survey

Materials selection is based on safety and economic considerations; the least expensive material securely withstanding service conditions for a required service time is chosen. For the integrity of equipment in the CPI chemical resistance is an essential factor. Of all metallic materials used for CPI equipment, tantalum is second to none regarding chemical inertness, comparing only to resistance properties of the nonmetals glass, fluoropolymers, and graphite. The price of tantalum, however, prohibits its broad application for construction. There are only two ways by which the demand for tantalum in this field can be promoted significantly. First, a major increase in the aggressivity of service conditions in process engineering caused by process development or modification. Second, cost reduction via tantalum price dilution by means of duplex systems application, utilizing the advantages of a less expensive base metal and a thin tantalum lining or coating. The more important systems of this type are discussed and evaluated regarding their potential of development.     

Hereditary macular dystrophies

BACKGROUND: Orthostatic hypotension is a common phenomenon in the elderly. Hormonal changes during orthostatic stress have been described in elderly normotensive people and in those with essential hypertension. However, the hormonal response in elderly people who have systolic hypertension during orthostasis has not yet been quantified. METHODS: In this study we investigated 14 non-diabetic men, aged 60 to 75 years, with untreated systolic hypertension who were subjected to 45 degrees passive head-up incline on a tilt table for 15 min. Their hormonal profile and hemodynamic changes were analyzed before and after the stress. RESULTS: In the supine position, plasma levels of norepinephrine, atrial natriuretic peptide and aldosterone were in the normal range, while the plasma renin activity was low. Immediately upon tilt the systolic blood pressure fell but it reverted to baseline values after 15 min of orthostasis. At that time the cardiac output decreased while the systemic vascular resistance and the plasma norepinephrine concentration rose. The atrial natriuretic peptide appeared to fall, and the renin-aldosterone level did not change. CONCLUSION: The physiologic response to orthostatic stress in elderly people with systolic hypertension is comparable to that of elderly normotensive people and those with essential hypertension, i.e. a decrease in cardiac output and an increase in plasma norepinephrine levels. The atrial natriuretic peptide appeared to fall appropriately. The response of the renin-aldosterone system mimicked that in elderly patients with low renin essential isolated hypertension. These observations may have a bearing on the management of elderly people with systolic hypertension who also have orthostatic symptoms; they may not require a different approach from that needed for others of the same age group.