Novel 1,2-dithiins: synthesis, molecular modeling studies, and antifungal activity.

The first structure-activity study involving the 1,2-dithiin class of compounds (1,2-dithiacyclohexadienes) is herein reported. A series of 3,6-disubstituted 1,2-dithiins was synthesized from dithiins 1d and 1e and evaluated as antifungal agents. A new and versatile synthesis of dithiins 1d and 1e is reported which is amenable to scale-up at the kilogram level. The novelty of the process derives from the use of beta-mercaptopropionitrile as the thiophile, relying on a beta-elimination strategy and subsequent oxidation to create the 1,2-dithiin ring. Optimal geometries of dithiins 1d, 18i, and 45 and model dithiin 61 were determined by molecular mechanics and Hartree-Fock molecular orbital calculations. Two possible mechanisms of action are presented for the 1,2-dithiin class of compounds to explain their observed antifungal activities against Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus.

Antihyperglycemic activities of cryptolepine analogues: an ethnobotanical lead structure isolated from Cryptolepis sanguinolenta.

Cryptolepine (1) is a rare example of a natural product whose synthesis was reported prior to its isolation from nature. In the previous paper we reported the discovery of cryptolepine's antihyperglycemic properties. As part of a medicinal chemistry program designed to optimize natural product lead structures originating from our ethnobotanical and ethnomedical field research, a series of substituted and heterosubstituted cryptolepine analogues was synthesized. Antihyperglycemic activity was measured in vitro and in an NIDDM mouse model to generate the first structure-bioactivity study about the cryptolepine nucleus.

Ethnobotanical-directed discovery of the antihyperglycemic properties of cryptolepine: its isolation from Cryptolepis sanguinolenta, synthesis, and in vitro and in vivo activities.

Using an ethnobotanical approach in combination with in vivo-guided fractionation as a means for lead discovery, cryptolepine was isolated as an antihyperglycemic component of Cryptolepis sanguinolenta. Two syntheses of cryptolepine, including an unambiguous synthesis, are reported. The hydroiodide, hydrochloride, and hydrotrifluoromethanesulfonate (hydrotriflate) salts of cryptolepine were synthesized, and a comparison of their spectral properties and their in vitro activities in a 3T3-L1 glucose transport assay is made. Cryptolepine and its salt forms lower blood glucose in rodent models of type II diabetes. While a number of bioactivities have been reported for cryptolepine, this is the first report that cryptolepine possesses antihyperglycemic properties.

Global health imaging curriculum in radiology residency programs: the fundamentals.

Recent advances in imaging technology have created new opportunities for medical imaging to improve health care in resource-restricted countries around the world. Radiology residents are increasingly interested in global health and imaging outreach, yet infrastructure and opportunities for international outreach are limited. With the recent change in the ABR exam schedule, residents now have more flexibility in the fourth year of training to pursue elective interests, including participation in global health projects. Creating a formalized global health imaging curriculum will improve the quality, quantity, and overall impact of initiatives undertaken by residents and their training programs. A curriculum is proposed that provides content, opportunities for global health project development, and established metrics for effective evaluation and assessment. Four components considered integral to a global health imaging curriculum are described: (1) global and public health education; (2) targeted travel medicine education; (3) basic imaging proficiency; and (4) practice attitudes and accountability. Methods are presented of differentiating curricula to increase applicability across the spectrum of training programs that vary in available resources. A blueprint is presented for formalizing a global health curriculum or elective rotation within a program, as well as a resource for residents, radiologists, and organizations to make a meaningful impact on global health.

Measurement of focal length using an optical power meter.

This Note shows that the focal length of a lens maybe calculated from the results of three radiometric measurements. The derived expression for focal length is valid for both positive and negative lenses.

Tilt correction in an optical disk system.

A servo system for the correction of disk tilt in optical disk data storage is proposed, and its basic concepts are demonstrated by the use of a static system in which the disk does not spin. Because disk tilt produces primarily coma in the beam focused onto the disk, the system uses a variable coma generator to produce an equal and opposite amount of coma as that caused by the tilted disk. The magnitude and direction of disk tilt are detected by the use of the light reflected from the front facet of the disk substrate.

Effects of substrate birefringence and tilt on the irradiance and phase patterns of the return beam in magneto-optical disk data storage.

Substrate birefringence in a magneto-optical disk system is shown to have a predictable effect on the return beam. The irradiance and phase patterns of the return beam at the exit pupil of the objective lens are calculated and experimentally verified for the cases of no substrate birefringence, birefringence aligned with the incident polarization, and birefringence aligned at 45° to the incident polarization. The irradiance at the exit pupil is also calculated (and experimentally verified) for a grooved substrate for various amounts of substrate tilt.

Compensation of chromatic errors in high na molded objective lenses.

High NA molded glass objective lenses are commercially available for use in the 680 nm to 850 nm range. We show that a simple positive lens can be used with an objective lens to compensate for wavelength-induced aberration in the 400 nm to 700 nm range. There is a direct relationship between the optimum power of the corrector lens and the wavelength of interest. We also show that a single positive lens and a holographic optical element can be used with an objective lens to compensate for wavelength-induced aberration over a wide range of wavelengths.

Dependence of the tracking performance of an optical disk on the direction of the incident-light polarization.

In optical-disk data-storage systems, the signal that provides tracking information is dependent on the groove shape, the optical constants of the materials involved, and the polarization state of the incident light. In this paper, we show that the tracking signal can be described by two measurable quantities, both of which are largely independent of aberrations in the optical system. Using these two quantities, we match the tracking performance of a given disk to an equivalent disk having rectangular grooves-the adjustable parameters being the rectangular groove depth and the duty cycle. By assumption, these rectangular grooves modulate only the phase of the incident beam and disregard its state of polarization. The effective groove depth and the duty cycle thus become dependent on the polarization state of the incident beam. We examine these dependences for various disks having different groove geometries and different combinations of materials.

Versatile objective lens with adjustable correction for different wavelengths and substrate thicknesses for testing optical disks.

A typical aspheric singlet used as the objective lens in optical-disk data-storage systems will not work at different wavelengths or with different substrate thicknesses because of spherochromatism. Using two microscope objectives with adjustable collars and a pair of relay lenses, we have constructed a system in which a diffraction-limited spot of any wavelength in the range of 0.4-0.7 mum can be moved by as much as +/-100 mum in both the focusing and tracking directions. We accomplished this by simply moving an aspheric singlet mounted in an off-the-shelf optical head. The system uses the adjustable collars of the microscope objectives to correct for the spherochromatism of the singlet and to accommodate the various thicknesses of the substrates.

Temperature dependence of the birefringence of optical-disk substrates.

Injection-molded polycarbonate substrates are used predominantly in read-only, write-once, phase-change and magneto-optic disks for data storage. The in-plane and vertical birefringences of these substrates adversely affect the performance of optical data-storage systems. The disks are typically expected to operate in the ambient temperature range of 5-50 °C. We have investigated the behavior of the in-plane and vertical birefringences of a polycarbonate disk substrate in this temperature range using a custom-built ellipsometer. This study reveals that the in-plane birefringence changes dramatically within the investigated range of temperatures, whereas the vertical birefringence remains essentially constant. We suspect that the change in birefringence is due primarily to thermally induced stress in the substrate.

Problem of track offset in optical disk systems.

In an optical disk drive, it is well known that a tilt of the disk causes an offset in the tracking-error signal (TES). One effect of disk tilt is the introduction of a dc component to the TES, which can be largely corrected by operation of the tracking system at the midpoint between the maximum and the minimum values of the open-loop TES. However, this method of correcting for the dc shift in the TES does not correct for the effect of coma in the focused spot, which leads to track offset. The track offset of a system is defined as the distance between the peak irradiance in the focused spot and the center of the groove when the tracking system is operating at the midpoint between the maximum and the minimum values of the open-loop TES in the presence of disk tilt. Calculations are performed that show the dependence of track offset on various system parameters, including track pitch, wavelength, and numerical aperture and rim intensity of the objective lens, and on the regions of the beam used to generate the TES. The track offsets for several beam-segmentation schemes are calculated for a digital versatile disk that uses push-pull and differential phase tracking. It is shown that for differential phase tracking the value of track offset depends on the mark length.

Effect of surface plasmon excitations on the irradiance pattern of the return beam in optical disk data storage.

The excitation of surface plasmons at a dielectric-metal interface is responsible for dips in the zeroth order diffraction efficiency of a metal grating at certain angles of incidence. The dips appear as dark bands in the returning irradiance pattern in an optical disk system and are seen only when there is a component of incident polarization that lies perpendicular to the tracks. The location of these bands is derived from theoretical considerations and is shown to depend on the track pitch and the materials involved, but not on the groove depth or width. The band locations are confirmed by zeroth order diffraction efficiency measurements as a function of incident angle. A possible negative effect of these bands on an optical disk system is the introduction of additional fluctuations and noise into the focusing and push-pull tracking signals.

Ring-lens focusing and push-pull tracking scheme for optical disk systems.

An experimental comparison of the ring-lens and the astigmatic techniques of generating a focus-error signal (FES) in optical disk systems reveals that the ring lens generates a FES curve over two times steeper than that produced by the astigmat. Partly because of this large slope and partly because of its diffraction-limited behavior, the ring-lens scheme exhibits superior performance characteristics. In particular, the undesirable signal known as feedthrough (induced on the FES by track crossings during the seek operation) is substantially lower than that observed with the astigmatic method. The ring lens is easy to align and has reasonable tolerance for positioning errors.

Versatile polychromatic dynamic testbed for optical disks.

A dynamic testbed for the evaluation of optical disks has been designed and constructed. The system is achromatic within the wavelength range 440-690 nm, allowing any light source in this range to be utilized for read-write-erase experiments. In addition, the system accepts disks with substrate thicknesses ranging from 0 to 1.7 mm. The polarization handling capabilities of the testbed are such that, with the turn of a knob, one can generate either linearly polarized or circularly polarized light at the disk surface. This feature permits the testing of both magneto-optical and phase-change disks, in addition to compact disks and digital versatile disks, without any modifications to the system. A leaky polarizing beam splitter (LPBS) has been specially designed and built for this tester. The LPBS allows continuous adjustment of the ratio between p- and s-polarized components of the reflected beam that reach the detectors. This feature is especially useful for magneto-optical disks, where one can achieve an optimum signal-to-noise ratio by adjusting the relative amounts of the two components of polarization at the detection module. Focus-error detection is based on the astigmatic method, and the primary track-error detection scheme is the push-pull method, although other focusing and tracking schemes may also be implemented. The rf data signal and the focusing and tracking servo signals are all derived from the same detectors, thus allowing the optical power returning from the disk to be used in its entirety for these multiple purposes. The detection channel consists of two high-speed quad detectors mounted on the two arms of a differential detection module. By combining the various outputs of these detectors it is possible to generate the astigmatic focus-error signal, the push-pull track-error signal, the differential magneto-optical readout signal, the conventional sum signal for phase-change disk readout, and the differential edge-signal for mark-edge detection on various types of optical media.

Synthetic analogues of irlbacholine: a novel antifungal plant metabolite isolated from Irlbachia alata.

Irlbacholine and a series of related analogues were synthesized and their antifungal activities against Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus were assessed. The natural bisphosphocholine, irlbacholine, was the most potent compound, its 22-carbon chain length appearing to be optimal.