Superelastic conducting fibers with improved properties and functionalities are needed for diverse applications. Here we report the fabrication of highly stretchable (up to 1320%) sheath-core ...conducting fibers created by wrapping carbon nanotube sheets oriented in the fiber direction on stretched rubber fiber cores. The resulting structure exhibited distinct short- and long-period sheath buckling that occurred reversibly out of phase in the axial and belt directions, enabling a resistance change of less than 5% for a 1000% stretch. By including other rubber and carbon nanotube sheath layers, we demonstrated strain sensors generating an 860% capacitance change and electrically powered torsional muscles operating reversibly by a coupled tension-to-torsion actuation mechanism. Using theory, we quantitatively explain the complementary effects of an increase in muscle length and a large positive Poisson's ratio on torsional actuation and electronic properties.
Carbon Nanotubes: The Route toward Applications Baughman, Ray H.; Zakhidov, Anvar A.; de Heer, Walt A.
Science (American Association for the Advancement of Science),
08/2002, Volume:
297, Issue:
5582
Journal Article
Peer reviewed
Many potential applications have been proposed for carbon nanotubes, including conductive and high-strength composites; energy storage and energy conversion devices, sensors; field emission displays ...and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects. Some of these applications are now realized in products. Others are demonstrated in early to advanced devices, and one, hydrogen storage, is clouded by controversy. Nanotube cost, polydispersity in nanotube type, and limitations in processing and assembly methods are important barriers for some applications of single-walled nanotubes.
Lymphocytic myocarditis causes left ventricular dysfunction that may be persistent or reversible. There are no clinical criteria that predict which patients will recover ventricular function and ...which cases will progress to dilated cardiomyopathy. We hypothesized that patients with fulminant myocarditis may have a better long-term prognosis than those with acute (nonfulminant) myocarditis.
We identified 147 patients considered to have myocarditis according to the findings on endomyocardial biopsy and the Dallas histopathological criteria. Fulminant myocarditis was diagnosed on the basis of clinical features at presentation, including the presence of severe hemodynamic compromise, rapid onset of symptoms, and fever. Patients with acute myocarditis did not have these features. The incidence of the end point of this study, death or heart transplantation, was ascertained by contact with the patient or the patient's family or by a search of the National Death Index. The average period of follow-up was 5.6 years.
A total of 15 patients met the criteria for fulminant myocarditis, and 132 met the criteria for acute myocarditis. Among the patients with fulminant myocarditis, 93 percent were alive without having received a heart transplant 11 years after biopsy (95 percent confidence interval, 59 to 99 percent), as compared with only 45 percent of those with acute myocarditis (95 percent confidence interval, 30 to 58 percent; P=0.05 by the log-rank test). Fulminant myocarditis was an independent predictor of survival after adjustments were made for age, histopathological findings, and hemodynamic variables. The rate of transplantation-free survival did not differ significantly between the patients considered to have borderline myocarditis and those considered to have active myocarditis according to the Dallas histopathological criteria.
Fulminant myocarditis is a distinct clinical entity with an excellent long-term prognosis. Aggressive hemodynamic support is warranted for patients with this condition.
The application of conducting polymers for the direct conversion of electrical energy to mechanical energy in electromechanical actuators is analyzed using theoretical and experimental results. Basic ...principles of operation, predicted performance advantages and disadvantages, comparisons with natural muscle, evaluations of initial device demonstrations, and methods for improving device performance are provided. The very high predicted work densities per cycle, force generation capabilities, and power densities provide major advantages compared with piezoelectric polymers – as do the low operation voltages. These advantages are countered by cycle life and energy conversion efficiency limitations, as well as the need to use microelectrodes in order to achieve very high rates. Hydrostatic devices and extensional devices that provide either in-phase or out-of-phase electrode deformations are considered. Special types of conducting polymer actuators are also proposed, including photo-powered, chemically powered and self-powered actuators, which provide novel methods for assembling complex microstructures. Novel methods are described for actuator fabrication, such as ‘redox poling’, wherein anode, cathode and separating electrolyte layers are generated from a film in a single redox step. New actuator compositions are also proposed for obtaining improved performance, such as conjugated carbon phases having conjugation in either two or three dimensions. Finally, conducting polymer actuators based on double-layer charging are proposed which are predicted to provide increased energy efficiency and cycle life compared with the faradaic actuators.
Polymer‐free carbon nanotube fibers are spun from aqueous dispersions using a flocculation‐based process that was developed. It produces hollow fibers, folded ribbon fibers, and solid fibers (see ...Figure). The fibers spun from single‐walled nanotubes exhibit relatively high electrical conductivities (∼140 S cm–1 at room temperature) and electrochemical capacitances (∼100 F g–1) after annealing. Fiber supercapacitors are made from the spun fibers.
By introducing twist during spinning of multiwalled carbon nanotubes from nanotube forests to make multi-ply, torque-stabilized yarns, we achieve yarn strengths greater than 460 megapascals. These ...yarns deform hysteretically over large strain ranges, reversibly providing up to 48% energy damping, and are nearly as tough as fibers used for bulletproof vests. Unlike ordinary fibers and yarns, these nanotube yarns are not degraded in strength by overhand knotting. They also retain their strength and flexibility after heating in air at 450°C for an hour or when immersed in liquid nitrogen. High creep resistance and high electrical conductivity are observed and are retained after polymer infiltration, which substantially increases yarn strength.
Previous studies of the prognosis of patients with heart failure due to cardiomyopathy categorized patients according to whether they had ischemic or nonischemic disease. The prognostic value of ...identifying more specific underlying causes of cardiomyopathy is unknown.
We evaluated the outcomes of 1230 patients with cardiomyopathy. The patients were grouped into the following categories according to underlying cause: idiopathic cardiomyopathy (616 patients), peripartum cardiomyopathy (51); and cardiomyopathy due to myocarditis (111), ischemic heart disease (91), infiltrative myocardial disease (59), hypertension (49), human immunodeficiency virus (HIV) infection (45), connective-tissue disease (39), substance abuse (37), therapy with doxorubicin (15), and other causes (117). Cox proportional-hazards analysis was used to assess the association between the underlying cause of cardiomyopathy and survival.
During a mean follow-up of 4.4 years, 417 patients died and 57 underwent cardiac transplantation. As compared with the patients with idiopathic cardiomyopathy, the patients with peripartum cardiomyopathy had better survival (adjusted hazard ratio for death, 0.31; 95 percent confidence interval, 0.09 to 0.98), and survival was significantly worse among the patients with cardiomyopathy due to infiltrative myocardial disease (adjusted hazard ratio, 4.40; 95 percent confidence interval, 3.04 to 6.39), HIV infection (adjusted hazard ratio, 5.86; 95 percent confidence interval, 3.92 to 8.77), therapy with doxorubicin (adjusted hazard ratio, 3.46; 95 percent confidence interval, 1.67 to 7.18), and ischemic heart disease (adjusted hazard ratio, 1.52; 95 percent confidence interval, 1.07 to 2.17).
The underlying cause of heart failure has prognostic value in patients with unexplained cardiomyopathy. Patients with peripartum cardiomyopathy appear to have a better prognosis than those with other forms of cardiomyopathy. Patients with cardiomyopathy due to infiltrative myocardial diseases, HIV infection, or doxorubicin therapy have an especially poor prognosis.
Individual carbon nanotubes are like minute bits of string, and many trillions of these invisible strings must be assembled to make useful macroscopic articles. We demonstrated such assembly at rates ...above 7 meters per minute by cooperatively rotating carbon nanotubes in vertically oriented nanotube arrays (forests) and made 5-centimeter-wide, meter-long transparent sheets. These self-supporting nanotube sheets are initially formed as a highly anisotropic electronically conducting aerogel that can be densified into strong sheets that are as thin as 50 nanometers. The measured gravimetric strength of orthogonally oriented sheet arrays exceeds that of sheets of high-strength steel. These nanotube sheets have been used in laboratory demonstrations for the microwave bonding of plastics and for making transparent, highly elastomeric electrodes; planar sources of polarized broad-band radiation; conducting appliqués; and flexible organic light-emitting diodes.
Carbon Nanotube Actuators Baughman, Ray H.; Cui, Changxing; Zakhidov, Anvar A. ...
Science,
05/1999, Volume:
284, Issue:
5418
Journal Article
Peer reviewed
Open access
Electromechanical actuators based on sheets of single-walled carbon nanotubes were shown to generate higher stresses than natural muscle and higher strains than high-modulus ferroelectrics. Like ...natural muscles, the macroscopic actuators are assemblies of billions of individual nanoscale actuators. The actuation mechanism (quantum chemical-based expansion due to electrochemical double-layer charging) does not require ion intercalation, which limits the life and rate of faradaic conducting polymer actuators. Unlike conventional ferroelectric actuators, low operating voltages of a few volts generate large actuator strains. Predictions based on measurements suggest that actuators using optimized nanotube sheets may eventually provide substantially higher work densities per cycle than any previously known technology.
We studied the femtosecond dynamics of photoexcitations in films containing semiconducting and metallic single-walled carbon nanotubes (SWNTs), using various pump-probe wavelengths and intensities. ...We found that confined excitons and charge carriers with subpicosecond dynamics dominate the ultrafast response in semiconducting and metallic SWNTs, respectively. Surprisingly, we also found from the exciton excited state absorption bands and multiphoton absorption resonances in the semiconducting nanotubes that transitions between subbands are allowed; this unravels the important role of electron-electron interaction in SWNT optics.
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