Electrical molecular switch addressed by chemical stimuli

We demonstrate that the conductance switching of benzo-bis(imidazole) molecules upon protonation depends on the lateral functional groups. The protonated H-substituted molecule shows a higher conductance than the neutral one (Gpro > Gneu), while the opposite (Gneu > Gpro) is observed for a molecule laterally functionalized by amino-phenyl groups. These results are demonstrated at various scale lengths: self-assembled monolayers, tiny nanodot-molecule junctions and single molecules. From ab initio theoretical calculations, we conclude that for the H-substituted molecule, the result Gpro > Gneu is correctly explained by a reduction of the LUMO-HOMO gap, while for the amino-phenyl functionnalized molecule, the result Gneu > Gpro is consistent with a shift of the HOMO, which reduces the density of states at the Fermi energy.

[Improving blood pressure control after a stroke: The place of therapeutic education in the acute phase]

OBJECTIVES

At the Paris Saint-Joseph Hospital Group neurovascular unit, the therapeutic patient education program "Treatment of high blood pressure after stroke" involved integrating a vascular physician. The objectives were to include a significant number of patients, to integrate learning self-measurement, and to make an initial analysis of the results concerning patient knowledge, self-measurement practices, adherence to treatment, and control of blood pressure.

METHODS

Eighty-six patients under 90 years of age admitted to the neurovascular unit were included in the program between January 1 and October 31, 2017, and participated in an in-hospital educational diagnostic interview followed by an initial session. During this period, 30 patients were reviewed within 3 to 6 months after discharge, with a post-session evaluation for 22 of them. Patient satisfaction was assessed with a questionnaire. A questionnaire was also proposed to the staff.

RESULTS

The mean blood pressure of the 22 patients reviewed was on target and they had improved their level of knowledge. The number of sphygmomanometers increased from 5 to 20, but the practice of cycles was not yet mastered. Levels of observed compliance changed little. Patients and paramedics appreciated the program and were convinced of its usefulness. These results do not support a direct effect of therapeutic patient education on blood pressure control, but the observed results are positive and encouraging.

Strain-induced bi-thermoelectricity in tapered carbon nanotubes

We show that carbon-based nanostructured materials are a novel testbed for controlling thermoelectricity and have the potential to underpin the development of new cost-effective environmentally-friendly thermoelectric materials. In single-molecule junctions, it is known that transport resonances associated with the discrete molecular levels play a key role in the thermoelectric performance, but such resonances have not been exploited in carbon nanotubes (CNTs). Here we study junctions formed from tapered CNTs and demonstrate that such structures possess transport resonances near the Fermi level, whose energetic location can be varied by applying strain, resulting in an ability to tune the sign of their Seebeck coefficient. These results reveal that tapered CNTs form a new class of bi-thermoelectric materials, exhibiting both positive and negative thermopower. This ability to change the sign of the Seebeck coefficient allows the thermovoltage in carbon-based thermoelectric devices to be boosted by placing CNTs with alternating-sign Seebeck coefficients in tandem.

Room temperature ballistic transport in InSb quantum well nanodevices

We report the room temperature observation of significant ballistic electron transport in shallow etched four-terminal mesoscopic devices fabricated on an InSb/AlInSb quantum well (QW) heterostructure with a crucial partitioned growth-buffer scheme. Ballistic electron transport is evidenced by a negative bend resistance signature which is quite clearly observed at 295 K and at current densities in excess of 10(6) A/cm(2). This demonstrates unequivocally that by using effective growth and processing strategies, room temperature ballistic effects can be exploited in InSb/AlInSb QWs at practical device dimensions.

Sub-100-nm negative bend resistance ballistic sensors for high spatial resolution magnetic field detection

We report the magnetic field detection properties of ballistic sensors utilizing the negative bend resistance of InSb∕In(1-x)Al(x)Sb quantum well cross junctions as a function of temperature and geometric size. We demonstrate that the maximum responsivity to magnetic field and its linearity increase as the critical device dimension is reduced. This observation deviates from the predictions of the classical billiard ball model unless significant diffuse boundary scattering is included. The smallest device studied has an active sensor area of 35×35 nm(2), with a maximum responsivity of 20 kΩ∕T, and a noise-equivalent field of 0.87μT∕Hz at 100 K.

Single-molecule solvation-shell sensing

We present a new route to single-molecule sensing via solvation shells surrounding a current-carrying backbone molecule. As an example, we show that the presence of a water solvation shell "gates" the conductance of a family of oligothiophene-containing molecular wires, and that the longer the oligothiophene, the larger is the effect. For the longest example studied, the molecular conductance is over 2 orders of magnitude larger in the presence of a shell comprising just 10 water molecules. A first principles theoretical investigation of electron transport through the molecules, using the nonequilibrium Green's function method, shows that water molecules interact directly with the thiophene rings, significantly shifting transport resonances and greatly increasing the conductance. This reversible effect is confirmed experimentally through conductance measurements performed in the presence of moist air and dry argon.

Non-trivial length dependence of the conductance and negative differential resistance in atomic molecular wires

We study the electronic and transport properties of two novel molecular wires made of atomic chains of carbon atoms (polyynes) capped with either benzene-thiols or pyridines. While both molecules are structurally similar, the electrical conductance of benzene-thiol-capped chains attached to gold electrodes is found to be much higher than that of pyridine-capped chains. We predict that the conductance is almost independent of molecular length, which suggests that these molecules could be ideal molecular wires for sub-10 nm circuitry. Both systems exhibit negative differential resistance (NDR) but its origin and characteristics depend on the type of molecule. We find a novel type of NDR mechanism produced by the movement of the lowest unoccupied molecular orbital (LUMO) resonance with bias. We also show that by gating the pyridine-capped molecules it is possible to make the NDR disappear and dramatically modify the I-V characteristics and the length dependence.

Carbon nanotube electron windmills: a novel design for nanomotors

We propose a new drive mechanism for carbon nanotube (CNT) motors, based upon the torque generated by a flux of electrons passing through a chiral nanotube. The structure of interest comprises a double-walled CNT formed from, for example, an achiral outer tube encompassing a chiral inner tube. Through a detailed analysis of electrons passing through such a "windmill," we find that the current, due to a potential difference applied to the outer CNT, generates sufficient torque to overcome the static and dynamic frictional forces that exist between the inner and outer walls, thereby causing the inner tube to rotate.

Quantum-classical correspondence in the wave functions of andreev billiards

We present a classical and quantum mechanical study of an Andreev billiard with a chaotic normal dot. We demonstrate that the nonexact velocity reversal and the diffraction at the edges of the normal-superconductor contact render the classical dynamics of these systems mixed indicating the limitations of a widely used retracing approximation. We point out the close relation between the mixed classical phase space and the properties of the quantum states of Andreev billiards, including periodic orbit scarring and localization of the wave function onto other classical phase space objects such as intermittent regions and quantized tori.

Conductance oscillations in zigzag platinum chains

Using first principles simulations we perform a detailed study of the structural, electronic, and transport properties of monatomic platinum chains, sandwiched between platinum electrodes. First, we demonstrate that the most stable atomic configuration corresponds to a zigzag arrangement that gradually straightens as the chains are stretched. Second, we find that the averaged conductance shows slight parity oscillations with the number of atoms in the chain. Additionally, the conductance of chains of fixed oscillates as the end atoms are pulled apart, due to the gradual closing and opening of conductance channels as the chain straightens.

Proximity-induced subgaps in andreev billiards

We examine the density of states of an Andreev billiard and show that any billiard with a finite upper cutoff in the path length distribution P(s) will possess an energy gap on the scale of the Thouless energy. An exact quantum mechanical calculation for different Andreev billiards gives good agreement with the semiclassical predictions when the energy dependent phase shift for Andreev reflections is properly taken into account. Based on this new semiclassical Bohr-Sommerfeld approximation of the density of states, we derive a simple formula for the energy gap. We show that the energy gap, in units of Thouless energy, may exceed the value predicted earlier from random matrix theory for chaotic billiards.

Negative length orbits in normal-superconductor billiard systems

The path-length spectra of mesoscopic systems including diffractive scatterers and connected to a superconductor are studied theoretically. We show that the spectra differ fundamentally from that of normal systems due to the presence of Andreev reflection. It is shown that negative path lengths should arise in the spectra as opposed to the normal system. To highlight this effect we carried out both quantum mechanical and semiclassical calculations for the simplest possible diffractive scatterer. The most pronounced peaks in the path-length spectra of the reflection amplitude are identified by the routes that the electron and/or hole travels.

Fractional quantum conductance in carbon nanotubes

Using a scattering technique based on a parametrized linear combination of atomic orbitals Hamiltonian, we calculate the ballistic quantum conductance of multiwall carbon nanotubes. We find that interwall interactions not only block some of the quantum conductance channels, but also redistribute the current nonuniformly over individual tubes across the structure. Our results provide a natural explanation for the unexpected integer and noninteger conductance values reported for multiwall nanotubes by Stefan Frank et al. [Stefan Frank et al., Science 280, 1744 (1998)].

Anomalous behavior of superconducting-normal mesoscopic structures near T(c)

We observe a maximum in the conductance of Al/n-GaAs junctions at temperatures 20 mK lower than the superconducting transition temperature (T(c)). This is the first observation of a peak in the conductance near the superconducting transition in superconducting-normal (S/N) junctions. To accommodate this effect we calculate the full temperature dependence of the conductance of these structures, invoking quasiclassical Green's functions in the diffusive limit. In addition to the well-known low-temperature peak at temperatures on the order of the Thouless energy, we find a maximum near T(c). This peak has the same origin as the subgap conductance observed in S/N junctions at low temperatures.

Video-assisted thoracoscopic surgery for management of spontaneous pneumothorax

Spontaneous pneumothorax is a common problem facing thoracic surgeons, occurring in about nine individuals per 100,000 each year. Treatment options include observation, chest tube thoracostomy, and thoracotomy with or without pleurodesis. When surgery is indicated, thoracoscopic surgery has been shown to provide excellent results with low morbidity, low recurrence, high patient acceptance, a shorter hospital stay and possibly decreased costs. In this article, we present the successful treatment of two cases of recurrent pneumothorax via video-assisted thoracoscopic surgery, combined with mechanical and chemical pleurodesis.

Trauma in pregnancy: the role of interpersonal violence

OBJECTIVE

Our purpose was to determine what role interpersonal violence as intentional injury plays in the pregnant trauma victim.

STUDY DESIGN

We performed a retrospective review of medical records.

RESULTS

During a 9-year period in a single university medical and trauma center, 203 pregnant women were treated for a physically traumatic event. Sixty-four women (31.5%) were victims of intentional injury, in most cases by the husband or boyfriend. Although the mean Injury Severity Score was higher in women with fetal death than in women with successful pregnancy outcomes (7.25 vs 1.74, respectively; p < 0.01), 5 of the 8 women with fetal losses incurred these despite an apparent absence of physical injury (maternal Injury Severity Score = 0).

CONCLUSIONS

Interpersonal violence during pregnancy is a frequent and increasingly common cause of maternal injury. The inconsistent relationship between Injury Severity Score and serious fetal injury or death is underscored by the loss of 5 fetuses despite an Injury Severity Score of 0.

Effect of a free radical scavenger on cadaver lung transplantation

The pulmonary donor pool would increase substantially if lungs could be safely transplanted after cessation of circulation. To determine whether the addition of the free radical scavenger dimethylthiourea to the perfusate of cadaver lungs could improve graft function, canine donors were sacrificed, and lungs retrieved 2 hours after death. In a blinded fashion, dimethylthiourea was added to the modified Euro-Collins solution and infused into recipients (n = 9) perioperatively; a placebo was included in the perfusate of control animals (n = 9). Donor animals were ventilated with 100% oxygen only during flush and harvest. Recipients were rendered dependent upon the single left transplanted lung by occlusion of the right pulmonary artery and bronchus 1 hour after transplantation. Ventilation was maintained at a constant inspiratory oxygen fraction of 0.4. Recipients were followed up for 8 hours or until death. Three of 9 control animals survived the 8-hour observation period, whereas 6 of 9 recipients of cadaver lungs harvested with dimethylthiourea survived the observation period. Two deaths in the dimethylthiourea group occurred after 7 hours, implying that the effects of the ischemia and reperfusion injury were ameliorated by the use of this agent in this model. This study supports the notion that perfusate modification may improve the yield of cadaver lung retrieval and may allow for transplantation of lungs harvested from cadavers after cessation of circulation.

Cadaver lung donors: effect of preharvest ventilation on graft function

The pulmonary donor pool would increase substantially if lungs could be safely transplanted after cessation of circulation. To determine whether ventilation of cadaver lungs could improve graft function, canine donors were sacrificed and then ventilated with 100% oxygen (n = 6) or 100% nitrogen (n = 6); 6 served as nonventilated controls. Four hours after death, the lungs were flushed with modified Euro-Collins solution and harvested. Controls were ventilated with 100% oxygen only during flush and harvest. Recipients were rendered dependent on the transplanted lung by occlusion of the right pulmonary artery and bronchus 1 hour after transplantation. Ventilation was maintained at a constant inspired oxygen fraction of 0.4. Four controls died of pulmonary edema shortly after occlusion of the native lung. The mean arterial oxygen tensions in the oxygen-ventilated, nitrogen-ventilated, and control groups at the end of 8 hours were 81 mm Hg (n = 4), 88 mm Hg (n = 3), and 55 mm Hg (n = 2), respectively. Postmortem oxygen ventilation improved early recipient survival and gas exchange. Postmortem nitrogen ventilation improved early gas exchange and delayed recipient death compared with non-ventilated controls. The mechanics of ventilation appears to confer a functional advantage independent of a continued supply of oxygen. Transplantation of lungs harvested from cadavers after cessation of circulation might be feasible.

Optimal timing of administration of a free radical scavenger in lung preservation

The optimal timing of administration of free radical scavengers in lung preservation has yet to be determined. In previous studies, the oxygen free radical scavenger dimethylthiourea (DMTU) has improved pulmonary function when added to Eurocollins flush solution at the time of lung harvest and infused at the time of lung reimplantation. To determine when DMTU must be administered in order to preserve lung function most effectively, 16 dogs underwent lung allotransplantation. Donor lungs were flushed with modified Eurocollins solution (50 ml/kg) and stored for 12 hr at 4 degrees C. DMTU was either added to the flush solution (5 g) or infused (20 g over 2 hr) at the time of reimplantation. Investigators were blinded to the time of DMTU administration. The contralateral pulmonary artery was ligated after a 1-hr stabilization period. Measurements were recorded for 8 hr while keeping FiO2 constant at 40%. The flush group demonstrated significantly improved survival and oxygenation compared with the infusion group. The mortality rate was 50% in the infusion treatment group, while no deaths occurred in the flush animals. Lung function is adequately preserved after 12-hr storage when DMTU is administered in the flush solution at the time of harvest. It would appear that oxygen free radical scavengers must be present in lung tissue during storage in order to be effective.

Isolated lung transplantation for end-stage lung disease: a viable therapy

Since January 1990, we have performed 29 isolated lung transplantations in 28 patients with end-stage lung disease (12 single, 16 bilateral). Recipient diagnoses were: cystic fibrosis (11), chronic obstructive pulmonary disease (6), pulmonary fibrosis (6), eosinophilic granulomatosis (1), postinfectious lung disease (1), adult respiratory distress syndrome (1), and primary pulmonary hypertension (2). There have been four deaths, two in patients with pulmonary fibrosis and two in patients with primary pulmonary hypertension. Four patients have undergone transplantation while on ventilatory support for respiratory failure (2 with cystic fibrosis, 1 having redo lung transplantation with cystic fibrosis, and 1 with adult respiratory distress syndrome); all of these have survived. Six patients required cardiopulmonary bypass, which was associated with increased transfusion requirement. All patients 2 months after discharge have returned to an active life-style, except for 2 patients who currently await retransplantation. Preoperative pulmonary rehabilitation has resulted in significant improvement in exercise performance in all patients. Immunosuppression consists of cyclosporine, azathioprine, and antilymphoblast globulin (University of Minnesota), withholding systemic steroids in the early postoperative period. We have employed bronchial omentopexy in all but four transplants; there has been one partial bronchial dehiscence, two instances of bronchomalacia requiring internal stenting, and one airway stenosis. Cytomegalovirus disease has been seen frequently (15 cases), but has responded well to treatment with ganciclovir. Other complication shave included one drug-related prolonged postoperative ventilation, thrombosis of a left lung after bilateral lung transplantation requiring retransplantation, five episodes of unilateral phrenic nerve palsy after bilateral lung transplantation (4 resolved), and the requirement of massive transfusion (greater than 10 units) in 5 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

A strategy to increase the donor pool: use of cadaver lungs for transplantation

A shortage of suitable donors is a serious obstacle to the widespread application of isolated lung transplantation for end-stage lung disease. We hypothesized that lung tissue likely remains viable for a sufficient period of time to allow for safe postmortem retrieval of lungs for transplantation. Studies were conducted in a nonsurvival model of canine lung allotransplantation. Donor animals were sacrificed, and subsequent lung harvest was delayed for 1 hour, 2 hours, or 4 hours. Pulmonary retrieval was then performed in a standard fashion, flushing the lung block with modified Euro-Collins solution. Lungs were then stored for 4 hours before single allotransplantation. Recipient animals were maintained anesthetized, and followed up for 8 hours. By occlusion of the pulmonary artery and bronchus to the native lung, recipient animals were forced to survive solely on the transplanted lung, with a constant inspired oxygen fraction of 0.40. All 5 recipient animals of 1-hour cadaver lungs survived the 8-hour observation period with excellent hemodynamics and gas exchange. Two of 5 recipients of 2-hour cadaver lungs survived the observation period, whereas a third animal survived for 5 hours with excellent gas exchange. One of 4 animals transplanted with a 4-hour cadaver lung survived the observation period. Retrieval of lungs from cadavers whose hearts are not beating may prove to be a safe and effective method to increase the pulmonary donor pool.

Enhanced pulmonary function using dimethylthiourea for twelve-hour lung preservation

Current preservation techniques for lung transplantation limit ischemic time to 6 hours. The purpose of this study was to evaluate the ability of dimethylthiourea, a low molecular weight free radical scavenger, to prolong this interval. An in vivo canine transplantation model was used to assess lung function. At harvest and after circulatory arrest, the donor lung was flushed with modified Euro-Collins solution (50 mL/kg). In a blinded fashion, dimethylthiourea (5 g) or saline solution was added to the flush solution at harvest and also infused (20 g over 2 hours) at reimplantation. Harvested lungs were stored for 12 hours at 4 degrees C. Allotransplantation was performed in recipient dogs ventilated with 40% O2. After 1 hour, the contralateral pulmonary artery was ligated, forcing the dog to be dependent on the transplanted lung. Twelve dogs were studied, with 6 randomly assigned to each treatment group in a blinded fashion. Measurements were recorded for 8 hours, keeping the inspired oxygen fraction constant at 0.40. All dimethylthiourea-treated dogs survived the observation period, whereas one third of the dogs that received saline solution died. Dimethylthiourea-treated dogs had significantly greater arterial oxygen tension and significantly less pulmonary vascular resistance compared with control animals. These results suggest that treatment of the lung with a free radical scavenger (dimethylthiourea) improves pulmonary function after reimplantation in a canine model after 12-hour hypothermic storage.

Splenic artery aneurysm. A rare cause of upper gastrointestinal bleeding

Most splenic artery aneurysms (SAAs) are asymptomatic at the time of discovery, being found incidentally during laparotomy or angiography. SAAs are most likely to be found in multiparous women. Complications of SAAs include free intraperitoneal rupture and erosion into abdominal viscera or vessels, with resultant high mortality. Surgery is indicated for symptomatic, enlarging, or large (greater than or equal to 2.5 cm) SAAs as well as any SAA found in women of childbearing age. Treatment of such aneurysms depends on the location and includes excision, ligation, and splenectomy. The present report presents the first known case, to our knowledge, of SAA presenting with massive upper gastrointestinal bleeding from erosion into the stomach in a nulliparous woman. Prompt surgical intervention resulted in correct diagnosis and patient survival.

Major hepatic resections: a 10-year experience with emphasis on special problems

From 1976-1985, 32 patients underwent major hepatic resection at the University of Mississippi Medical Center. This experience was reviewed to determine the relationship of blood loss, postoperative hyperbilirubinemia, and the performance of concomitant surgical procedures to operative mortality, local tumor recurrence, and long-term survival. There were no deaths among 16 elective resections. Of 16 patients undergoing emergency resections, seven died (43.8%). The mortality rate correlated strongly with intraoperative transfusion of more than 10 units of blood and with postoperative hyperbilirubinemia. Performance of additional procedures increased mortality significantly after emergency, but not elective, hepatic resection. Median survival was 53.4 months in patients resected for hepatoma and 33.5 months in those patients resected for metastatic colon lesions. Local recurrence in a patient with hepatoma was managed by resection at 13 months, with no evidence of further recurrence at 69 months.

The treatment of postperfusion bleeding using epsilon-aminocaproic acid, cryoprecipitate, fresh-frozen plasma, and protamine sulfate

The evaluation of excessive hemorrhage was carried out in 774 patients after cardiopulmonary bypass. Excessive hemorrhage was defined in any adult patient as chest tube drainage of more than 600 ml within the first eight hours after operation. Using the prothrombin time, partial thromboplastin time, fibrinogen level, and tri-F titer tests, it was possible to differentiate medical from surgical bleeding. Hyperfibrinolytic bleeding was the most frequently identifiable coagulation disorder and occurred in 159 patients (20%). All these patients were successfully treated with Amicar (epsilon-aminocaproic acid) alone, or with Amicar supplemented with cryoprecipitate or fresh-frozen plasma. Three patients (0.4%) were noted to have residual heparin and required additional protamine sulfate. Five patients (0.6%) had normal coagulation studies and required immediate reexploration. The overall blood consumption per patient was 2.1 units of packed cells. Whole blood and platelets were not used.