A coherent nanomechanical oscillator driven by single-electron tunnelling

A single-electron transistor embedded in a nanomechanical resonator represents an extreme limit of electron-phonon coupling. While it allows fast and sensitive electromechanical measurements, it also introduces backaction forces from electron tunnelling that randomly perturb the mechanical state. Despite the stochastic nature of this backaction, it has been predicted to create self-sustaining coherent mechanical oscillations under strong coupling conditions. Here, we verify this prediction using real-time measurements of a vibrating carbon nanotube transistor. This electromechanical oscillator has some similarities with a laser. The single-electron transistor pumped by an electrical bias acts as a gain medium and the resonator acts as a phonon cavity. Although the operating principle is unconventional because it does not involve stimulated emission, we confirm that the output is coherent. We demonstrate other analogues of laser behaviour, including injection locking, classical squeezing through anharmonicity, and frequency narrowing through feedback.

Drilling systems for extraterrestrial subsurface exploration

Drilling consists of 2 processes: breaking the formation with a bit and removing the drilled cuttings. In rotary drilling, rotational speed and weight on bit are used to control drilling, and the optimization of these parameters can markedly improve drilling performance. Although fluids are used for cuttings removal in terrestrial drilling, most planetary drilling systems conduct dry drilling with an auger. Chip removal via water-ice sublimation (when excavating water-ice-bound formations at pressure below the triple point of water) and pneumatic systems are also possible. Pneumatic systems use the gas or vaporization products of a high-density liquid brought from Earth, gas provided by an in situ compressor, or combustion products of a monopropellant. Drill bits can be divided into coring bits, which excavate an annular shaped hole, and full-faced bits. While cylindrical cores are generally superior as scientific samples, and coring drills have better performance characteristics, full-faced bits are simpler systems because the handling of a core requires a very complex robotic mechanism. The greatest constraints to extraterrestrial drilling are (1) the extreme environmental conditions, such as temperature, dust, and pressure; (2) the light-time communications delay, which necessitates highly autonomous systems; and (3) the mission and science constraints, such as mass and power budgets and the types of drilled samples needed for scientific analysis. A classification scheme based on drilling depth is proposed. Each of the 4 depth categories (surface drills, 1-meter class drills, 10-meter class drills, and deep drills) has distinct technological profiles and scientific ramifications.

Retrieval of an endobronchial foreign body using a guide wire and angioplasty catheter

We report the use of a guide wire and angioplasty balloon catheter to retrieve an endobronchial foreign body after failure of conventional techniques. The foreign body was a pen top that had a small lumen, which allowed passage of the wire and use of the balloon catheter for retrieval. The difficulty of retrieval of such objects and the limitations of the equipment usually used for this procedure are discussed.

Use of computed tomography pulmonary angiography in the diagnosis of pulmonary embolismin patients with an intermediate probability ventilation/perfusion scan

BACKGROUND

Computed tomography pulmonary -angiography (CTPA) plays an increasingly important role in the diagnosis of pulmonary embolism (PE). Although accurate in the detection of large PE, its accuracy in other patient groups is yet to be defined.

AIM

To compare CTPA with pulmonary angiography as a second-line investigation in patients with a ventilation/perfusion (VQ) scan indicating an intermediate probability of PE.

METHODS

We recruited 25 patients over a 17-month period. Subjects were eligible if they: (i). had clinically suspected PE, (ii). had a VQ scan indicating an intermediate probability of PE and (iii). were referred for pulmonary angiography. Subjects underwent CTPA within 36 h of the VQ scan. CTPA was interpreted without knowledge of the results of the pulmonary angiogram by two of the authors.

RESULTS

PE was prevalent (i.e. embolus detected at pulmonary angiography) in seven of 25 subjects (28%). The sensitivity of CTPA was 57% and the specificity was 94%.

CONCLUSIONS

In the setting of intermediate-probability VQ scanning, CTPA may be used to clarify the diagnosis of PE. However, a negative CTPA cannot -definitely exclude PE. Conventional pulmonary angiography may be necessary to determine the presence of PE if CTPA is negative.

Diagnosis of breast cancer using elastic-scattering spectroscopy: preliminary clinical results

We report on the first stages of a clinical study designed to test elastic-scattering spectroscopy, mediated by fiberoptic probes, for three specific clinical applications in breast-tissue diagnosis: (1) a transdermal-needle (interstitial) measurement for instant diagnosis with minimal invasiveness similar to fine-needle aspiration but with sensitivity to a larger tissue volume, (2) a hand-held diagnostic probe for use in assessing tumor/resection margins during open surgery, and (3) use of the same probe for real-time assessment of the "sentinel" node during surgery to determine the presence or absence of tumor (metastatic). Preliminary results from in vivo measurements on 31 women are encouraging. Optical spectra were measured on 72 histology sites in breast tissue, and 54 histology sites in sentinel nodes. Two different artificial intelligence methods of spectral classification were studied. Artificial neural networks yielded sensitivities of 69% and 58%, and specificities of 85% and 93%, for breast tissue and sentinel nodes, respectively. Hierarchical cluster analysis yielded sensitivities of 67% and 91%, and specificities of 79% and 77%, for breast tissue and sentinel nodes, respectively. These values are expected to improve as the data sets continue to grow and more sophisticated data preprocessing is employed. The study will enroll up to 400 patients over the next two years.

Relaxivity of Gd-EOB-DTPA in the normal and biliary obstructed guinea pig

After injection of Gd-EOB-DTPA, T1 and T2 were determined on a clinical MR scanner (1.5 T) in the liver and kidneys of sacrificed but intact guinea pigs with normal and obstructed biliary systems and in bile, urine, and blood collected postmortem. Tissue [Gd] was determined by radioassay of 153Gd and relaxivities (R1 and R2; units of s(-1) x mmol(-1) x kg) of Gd-EOB-DTPA calculated. Compared with R1 in 2% agarose gel (4.49 +/- 0.03), in normal animals R1 was increased in liver (9.3 +/- 0.5), similar in kidney cortex (4.1 +/- 0.5), but reduced in kidney medulla (2.5 +/- 0.4) and papilla (2.7 +/- 0.4). Chronic biliary obstruction did not change R1 in liver (9.7 +/- 4.3) but reduced R1 further in kidney tissues (1.0-0.4). In normal animals, R2 values of all tissues (9.5-18.4) were greater than R2 in gel (5.72 +/- 0.12). Biliary obstruction possibly elevated R2 in liver (40.1 +/- 63.5), severely depressed R2 in kidney cortex (-4.2 +/- 6.2) and medulla (-2.3 +/- 5.4), and reduced R2 in papilla (5.4 +/- 4.6). Obstruction had little effect on R1 and R2 in bile and urine. Water content, macromolecular binding, microviscosity, compartmentalization, and susceptibility effects can readily account for the R1 and R2 observed in liver and kidney. Negative R2 could be a result of several factors, including reduced endogenous magnetic field gradients due to "susceptibility matching" as [Gd] increased, changes in tissue T2 with period of ligation, or a physiological effect of EOB-DTPA. These results show that disease can alter both R1 and R2 from their values in normal tissues.

Season of birth of schizophrenics in Mississippi, USA

Prior reviews indicate that schizophrenics tend to be born in the winter, relative to non-psychiatric controls. This conclusion has been criticized, however, as the association between birth seasonality and schizophrenia may be the result of a statistical artifact, the age-incidence effect. To examine this possibility, we studied the birth seasonality of 2892 schizophrenics, controlling for the age-incidence effect. Both before and after instituting these controls, we found excesses for the months of December and March. We conclude that the age-incidence hypothesis does not provide any general explanation of the season-of-birth effect in schizophrenia.

Differences between schizophrenics born in winter and summer

A total of 1814 patients were studied from the Mississippi State Hospital with a DSM-III diagnosis of schizophrenia and aged 15-39 years at the time of admission. The 634 schizophrenics with a birth date between 1 December and 31 March were compared with the 1180 born between 1 April and 30 November for age of admission, race, sex, marital status, duration of initial admission and clinical subtype. The only significant difference between the variables was the duration of the first admission: winter-born patients had a shorter psychiatric hospitalization than summer-born schizophrenics. These findings are discussed in accord with similar studies.

An inducible gene expression system for Neurospora crassa

Neurospora crassa acetyl CoA synthetase is highly induced when the growing mycelium is transferred from sucrose- to acetate-based medium. The inducible promoter of this gene has been isolated and used to control the expression of glutamate dehydrogenase. Transformants containing this expression cassette show gdh levels up to 25 times higher than the nontransformed host strain. This expression cassette will form the basis of a system of heterologous gene expression.

Mutagenicity of substituted carbazoles in Salmonella typhimurium

Mutagenic activities of 1-, 2-, 3-, 4-, and 9-methylcarbazole were evaluated in S. typhimurium TA1535, TA1537, TA1538, TA98, and TA100. Only 9-methylcarbazole was found to be mutagenic in S. typhimurium TA100 in the presence of rat-liver homogenate. Mutagenic activity was also observed in TA100 for 2,9-, 3,9-, and 4,9-dimethylcarbazole. None of these methylated carbazole derivatives was mutagenic in TA1535, TA1537, TA1538 and TA98 in either the presence of absence of rat-liver homogenate. These results indicate that a 9-methyl substituent is associated with the mutagenic activity of these carbazole derivatives. Comparative studies on the mutagenic activity of 9-substituted carbazoles demonstrated that the activity of 9-ethylcarbazole was less than that of 9-methylcarbazole. 9-Phenyl- and 9-i-propylcarbazole were inactive under identical assay conditions. 9-Hydroxymethylcarbazole, a major metabolite of 9-methylcarbazole, was confirmed to be a direct-acting mutagen in S. typhimurium TA100. 9-Formylcarbazole was inactive as a mutagen when assayed with or without metabolic activation. These data are consistent with the finding that 9-hydroxymethylcarbazole is a major proximate mutagenic form of 9-methylcarbazole.

A New Look at the Saturn System: The Voyager 2 Images

Voyager 2 photography has complemented that of Voyager I in revealing many additional characteristics of Saturn and its satellites and rings. Saturn's atmosphere contains persistent oval cloud features reminiscent of features on Jupiter. Smaller irregular features track out a pattern of zonal winds that is symmetric about Saturn's equator and appears to extend to great depth. Winds are predominantly eastward and reach 500 meters per second at the equator. Titan has several haze layers with significantly varying optical properties and a northern polar "collar" that is dark at short wavelengths. Several satellites have been photographed at substantially improved resolution. Enceladus' surface ranges from old, densely cratered terrain to relatively young, uncratered plains crossed by grooves and faults. Tethys has a crater 400 kilometers in diameter whose floor has domed to match Tethys' surface curvature and a deep trench that extends at least 270 degrees around Tethys' circumference. Hyperion is cratered and irregular in shape. Iapetus' bright, trailing hemisphere includes several dark-floored craters, and Phoebe has a very low albedo and rotates in the direction opposite to that of its orbital revolution with a period of 9 hours. Within Saturn's rings, the "birth" of a spoke has been observed, and surprising azimuthal and time variability is found in the ringlet structure of the outer B ring. These observations lead to speculations about Saturn's internal structure and about the collisional and thermal history of the rings and satellites.

Mutagenicity of aminocarbazoles and nitrocarbazoles

The mutagenic activity of all 4 isomeric aminocarbazoles and 4 nitrocarbazoles was evaluated in Salmonella typhimurium tester strains TA98. TA100 and TA1535. All compounds were assayed both in the presence and absence of liver homogenate from Aroclor-treated rats. Among the aminocarbazoles, 2-aminocarbazole was found to be most active in both tester strains, although somewhat less active than 2-aminofluorene. 3-Aminocarbazole was the only other isomer that was mutagenic towards TA98 at the dose levels employed (5--200 micrograms). 4-Aminocarbazole was moderately active in TA100, and 1-aminocarbazole was inactive in both TA98 and TA100. Similar differences in mutagenic potency and specificity towards the tester strains were observed for the related series of nitrocarbazoles.

Encounter with Saturn: Voyager 1 Imaging Science Results

As Voyager 1 flew through the Saturn system it returned photographs revealing many new and surprising characteristics of this complicated community of bodies. Saturn's atmosphere has numerous, low-contrast, discrete cloud features and a pattern of circulation significantly different from that of Jupiter. Titan is shrouded in a haze layer that varies in thickness and appearance. Among the icy satellites there is considerable variety in density, albedo, and surface morphology and substantial evidence for endogenic surface modification. Trends in density and crater characteristics are quite unlike those of the Galilean satellites. Small inner satellites, three of which were discovered in Voyager images, interact gravitationally with one another and with the ring particles in ways not observed elsewhere in the solar system. Saturn's broad A, B, and C rings contain hundreds of "ringlets," and in the densest portion of the B ring there are numerous nonaxisymmetric features. The narrow F ring has three components which, in at least one instance, are kinked and crisscrossed. Two rings are observed beyond the F ring, and material is seen between the C ring and the planet.

The Galilean Satellites and Jupiter: Voyager 2 Imaging Science Results

Voyager 2, during its encounter with the Jupiter system, provided images that both complement and supplement in important ways the Voyager 1 images. While many changes have been observed in Jupiter's visual appearance, few, yet significant, changes have been detected in the principal atmospheric currents. Jupiter's ring system is strongly forward scattering at visual wavelengths and consists of a narrow annulus of highest particle density, within which is a broader region in which the density is lower. On Io, changes are observed in eruptive activity, plume structure, and surface albedo patterns. Europa's surface retains little or no record of intense meteorite bombardment, but does reveal a complex and, as yet, little-understood system of overlapping bright and dark linear features. Ganymede is found to have at least one unit of heavily cratered terrain on a surface that otherwise suggests widespread tectonism. Except for two large ringed basins, Callisto's entire surface is heavily cratered.