Suppression of crosstalk in multielectrode arrays with local shielding

Electrical crosstalk can constrain the performance of multielectrode arrays in electro- and neurophysiology, in terms of both stimulation and recording. This is especially so at high electrode density, desirable for spatiotemporal mapping of bioelectrical signals from multiple cells. Channel interference due to crosstalk is currently only partially addressed, via continuous interleaved sampling or post-data acquisition spike sorting. Here, we show that a locally-shielded electrode architecture significantly suppresses crosstalk, and enables multi-site recording at high electrode density without the need for spike sorting. Arrays of shielded electrodes, prepared by micro- and nanofabrication techniques in a vertically-oriented coaxial geometry, demonstrate at least a 400 times improvement in spatial density over the unshielded case.

Towards spectrally selective catastrophic response

We study the large-amplitude response of classical molecules to electromagnetic radiation, showing the universality of the transition from linear to nonlinear response and breakup at sufficiently large amplitudes. We demonstrate that a range of models, from the simple harmonic oscillator to the successful Peyrard-Bishop-Dauxois type models of DNA, which include realistic effects of the environment (including damping and dephasing due to thermal fluctuations), lead to characteristic universal behavior: formation of domains of dissociation in driving force amplitude-frequency space, characterized by the presence of local boundary minima. We demonstrate that by simply following the progression of the resonance maxima in this space, while gradually increasing intensity of the radiation, one must necessarily arrive at one of these minima, i.e., a point where the ultrahigh spectral selectivity is retained. We show that this universal property, applicable to other oscillatory systems, is a consequence of the fact that these models belong to the fold catastrophe universality class of Thom's catastrophe theory. This in turn implies that for most biostructures, including DNA, high spectral sensitivity near the onset of the denaturation processes can be expected. Such spectrally selective molecular denaturation could find important applications in biology and medicine.

Anomalous Acoustic Plasmon Mode from Topologically Protected States

Plasmons, the collective excitations of electrons in the bulk or at the surface, play an important role in the properties of materials, and have generated the field of "plasmonics." We report the observation of a highly unusual acoustic plasmon mode on the surface of a three-dimensional topological insulator (TI) Bi_{2}Se_{3}, using momentum resolved inelastic electron scattering. In sharp contrast to ordinary plasmon modes, this mode exhibits almost linear dispersion into the second Brillouin zone and remains prominent with remarkably weak damping not seen in any other systems. This behavior must be associated with the inherent robustness of the electrons in the TI surface state, so that not only the surface Dirac states but also their collective excitations are topologically protected. On the other hand, this mode has much smaller energy dispersion than expected from a continuous media excitation picture, which can be attributed to the strong coupling with surface phonons.

Hot electron plasmon-protected solar cell

A solar cell based on a hot electron plasmon protection effect is proposed and made plausible by simulations, non-local modeling of the response, and quantum mechanical calculations. In this cell, a thin-film, plasmonic metamaterial structure acts as both an efficient photon absorber in the visible frequency range and a plasmonic resonator in the IR range, the latter of which absorbs and protects against phonon emission the free energy of the hot electrons in an adjacent semiconductor junction. We show that in this structure, electron-plasmon scattering is much more efficient than electron-phonon scattering in cooling-off hot electrons, and the plasmon-stored energy is recoverable as an additional cell voltage. The proposed structure could become a prototype of a new generation of high efficiency solar cells.

Spectroscopic evidence for negative electronic compressibility in a quasi-three-dimensional spin-orbit correlated metal

Negative compressibility is a sign of thermodynamic instability of open or non-equilibrium systems. In quantum materials consisting of multiple mutually coupled subsystems, the compressibility of one subsystem can be negative if it is countered by positive compressibility of the others. Manifestations of this effect have so far been limited to low-dimensional dilute electron systems. Here, we present evidence from angle-resolved photoemission spectroscopy (ARPES) for negative electronic compressibility (NEC) in the quasi-three-dimensional (3D) spin-orbit correlated metal (Sr1-xLax)3Ir2O7. Increased electron filling accompanies an anomalous decrease of the chemical potential, as indicated by the overall movement of the deep valence bands. Such anomaly, suggestive of NEC, is shown to be primarily driven by the lowering in energy of the conduction band as the correlated bandgap reduces. Our finding points to a distinct pathway towards an uncharted territory of NEC featuring bulk correlated metals with unique potential for applications in low-power nanoelectronics and novel metamaterials.

Effects of downhill and uphill exercises of equivalent submaximal intensities on selected blood cytokine levels and blood creatine kinase activity

The study was aimed at comparing the effects of concentric (CONC) and eccentric (ECC) exercises of equivalent (in terms of relative work load expressed as a percentage of VO2max) moderate intensity on selected blood cytokine levels and blood creatine kinase (CK) activity. Twenty recreationally active healthy young male volunteers were randomized between two groups that performed a single 1 h bout of CONC (uphill running) or ECC (downhill running) exercise at 60% of the respective individual VO2max. Venous blood taken 1 h before, at the end, and 24 h after the exercise was processed for plasma and analyzed for CK activity and IL-6, IL-1β and TNFα levels. There was no between-group difference in these cytokines prior to or just after the exercise, and in pre-exercise CK activity. The cytokines elevated significantly and similarly in both groups during the exercise, with no significant change in CK activity. Twenty-four hours later, CK activity and IL-6 were at pre-exercise levels in the CONC group, but showed further major increases in the ECC group, resulting in marked between-group differences in these indices. Changes in IL-1β and TNFα levels during the recovery period showed only minor differences between the study groups and produced no significant between-group difference in these cytokines. However, IL-1β level normalized in the ECC but not in the CONC group. The study suggests that moderate intensity ECC exercise compared to CONC exercise of equivalent relative work load results in considerably greater muscle damage and its related elevation in circulating IL-6, but it does not cause a major systemic inflammatory response.

Nanoscope based on nanowaveguides

The far field spatial resolution of conventional optical lenses is of the order of the wavelength of light, due to loss in the far field of evanescent, near electromagnetic field components. We show that subwavelength details can be restored in the far field with an array of divergent nanowaveguides, which map the discretized, subwavelength image of an object into a magnified image observable with a conventional optical microscope. We demonstrate in simulations that metallic nanowires, nanocoaxes, and nanogrooves can be used as such nanowaveguides. Thus, an optical microscope capable of subwavelength resolution - a nanoscope - can be produced, with possible applications in a variety of fields where nanoscale optical imaging is of value.

Interaction between carbon nanotubes and mammalian cells: characterization by flow cytometry and application

We show herein that CNT-cell complexes are formed in the presence of a magnetic field. The complexes were analyzed by flow cytometry as a quantitative method for monitoring the physical interactions between CNTs and cells. We observed an increase in side scattering signals, where the amplitude was proportional to the amount of CNTs that are associated with cells. Even after the formation of CNT-cell complexes, cell viability was not significantly decreased. The association between CNTs and cells was strong enough to be used for manipulating the complexes and thereby conducting cell separation with magnetic force. In addition, the CNT-cell complexes were also utilized to facilitate electroporation. We observed a time constant from CNT-cell complexes but not from cells alone, indicating a high level of pore formation in cell membranes. Experimentally, we achieved the expression of enhanced green fluorescence protein by using a low electroporation voltage after the formation of CNT-cell complexes. These results suggest that higher transfection efficiency, lower electroporation voltage, and miniaturized setup dimension of electroporation may be accomplished through the CNT strategy outlined herein.

Effects of castration and testosterone replacement on the antioxidant defense system in rat left ventricle

There is strong evidence that oxidative stress plays a key role in the pathophysiology of several cardiovascular diseases. On the other hand, the presence of specific receptors for androgens and estrogens in the myocardium implies that sex hormones play a physiological role in cardiac function, myocardial injury, and the regulation of the redox state in the heart. The present study was designed to determine whether castration and androgen replacement result in changes in the capacity of the antioxidant defense system in the left ventricle (LV) of adult male rats. To assess this, the activities of antioxidant enzymes (superoxide dismutase [SOD], glutathione peroxidase [GPX], catalase [CAT], and glutathione reductase [GR]), concentrations of nonenzymatic antioxidants (reduced glutathione [GSH] and alpha- and gamma-tocopherols), and oxidative stress biomarkers (tissue sulfhydryl groups, protein nitrotyrosine levels, and lipid peroxidation) were measured in castrated animals (CAS), castrates replaced with testosterone (CAS+T), and sham-operated controls (Sham). Testosterone was not detectable in serum from gonadectomized rats. The results indicate that castration significantly and negatively affected the antioxidant status of rat LV, as evidenced by a significant decline in activities of all antioxidant enzymes, by a tendency toward lower levels of GSH and protein thiol groups, and by enhanced lipid peroxidation and higher nitrotyrosine concentrations in left ventricular tissue. Increases in LV tissue concentrations of alpha- and gamma-tocopherols seem to be a compensatory response to enhanced oxidative stress induced by gonadectomy. The reestablishment of physiological serum testosterone level by androgen replacement resulted in a tendency toward a further decrease in the antioxidant defense status in the LV tissue.

TEM-like optical mode of a coaxial nanowaveguide

We study propagation of electromagnetic waves in a nanocoaxial waveguide for frequencies around and below the surface plasmon frequency. We show, that for frequencies sufficiently lower than the surface plasmon frequency, the waveguide supports a plasmon polariton mode that resembles, and indeed reduces to the conventional TEM mode of the conventional coaxial transmission line, known in the radiotechnology.

Optical transmission through hexagonal arrays of subwavelength holes in thin metal films

We have studied the light transmission through hexagonal arrays of subwavelength holes in thin gold and aluminum films, varying the film thickness between 20 and 120 nm while the hole diameter as well as the interhole distance have been kept constant at approximately 300 and approximately 500 nm, respectively. The films were characterized by means of UV-vis spectroscopy and scanning near-field optical microscopy (SNOM).

Enhanced ductile behavior of tensile-elongated individual double-walled and triple-walled carbon nanotubes at high temperatures

We report exceptional ductile behavior in individual double-walled and triple-walled carbon nanotubes at temperatures above 2000 degrees C, with tensile elongation of 190% and diameter reduction of 90%, during in situ tensile-loading experiments conducted inside a high-resolution transmission electron microscope. Concurrent atomic-scale microstructure observations reveal that the superelongation is attributed to a high temperature creep deformation mechanism mediated by atom or vacancy diffusion, dislocation climb, and kink motion at high temperatures. The superelongation in double-walled and triple-walled carbon nanotubes, the creep deformation mechanism, and dislocation climb in carbon nanotubes are reported here for the first time.

Superplastic carbon nanotubes

The theoretical maximum tensile strain--that is, elongation--of a single-walled carbon nanotube is almost 20%, but in practice only 6% is achieved. Here we show that, at high temperatures, individual single-walled carbon nanotubes can undergo superplastic deformation, becoming nearly 280% longer and 15 times narrower before breaking. This superplastic deformation is the result of the nucleation and motion of kinks in the structure, and could prove useful in helping to strengthen and toughen ceramics and other nanocomposites at high temperatures.

Nanomechanical properties of silica-coated multiwall carbon nanotubes-poly(methyl methacrylate) composites

The mechanical properties of polymer composites, reinforced with silica-coated multiwall carbon nanotubes (MWNTs), have been studied using the nanoindentation technique. The hardness and the Young's modulus have been found to increase strongly with the increasing content of these nanotubes in the polymer matrix. Similar experiments conducted on thin films containing MWNTs, but without a silica shell, revealed that the presence of these nanotubes does not affect the nanomechanical properties of the composites. While carbon nanotubes (CNTs) have a very high tensile strength due to the nanotube stiffness, composites fabricated with CNTs may exhibit inferior toughness. The silica shell on the surface of a nanotube enhances its stiffness and rigidity. Our composites, at 4 wt % of the silica-coated MWNTs, display a maximum hardness of 120 +/- 20 MPa, and a Young's modulus of 9 +/- 1 GPa. These are respectively 2 and 3 times higher than those for the polymeric matrix. Here, we describe a method for the silica coating of MWNTs. This is a simple and efficient technique, adaptable to large-scale production, and might lead to new advanced polymer based materials, with very high axial and bending strength.

Evaluation of Autoantibodies Against Oxidized LDL (oLAB) and Blood Antioxidant Status in Professional Soccer Players

Low-density lipoproteins (LDL) are very sensitive to oxidative processes initiated by oxygen free radicals, known to be produced in large quantities during intense physical exercise. Oxidatively modified lipoprotein particles (oxLDL) are strongly atherogenic and immunogenic, as a consequence specific autoantibodies (oLAB) against oxLDL are produced by the immune system. This study was designed to evaluate the oLAB titres in professional soccer players and to find out whether the immune response to oxidative modification of LDL correlates with the antioxidant status of individual players. Eleven players volunteered to participate in an incremental treadmill running exercise to volitional fatigue twice (in October and January) during the competitive season. Venous blood samples were withdrawn before and 3 min after the cessation of the test. Serum levels of oLAB were measured by ELISA (Biomedica). Blood samples were analyzed for glutathione peroxidase, reduced glutathione, superoxide dismutase, catalase and glutathione reductase. The activity of creatine kinase (CK) and concentrations of malondialdehyde (MDA), vitamin E and retinol were determined in plasma. From 11 subjects only in 4 players, in both graded running tests, the oLAB titres were low (< 200 mU.ml(-1)). The remaining athletes presented elevated oLAB (800-1400 mU.ml(-1)). Significantly lower activities of catalase and glutathione reductase and lower concentration of alpha-tocopherol were recorded in the 2nd trial. When the data were arranged according to the oLAB titres no significant between-group differences were found in either pre- and post-test activities of antioxidant enzymes or in concentrations of antioxidants. However, significantly higher CK activities and a tendency towards more elevated plasma MDA concentrations were observed in subjects with higher oLAB levels. It seems justified to presume that high titres of antibodies against oxLDL, as evidenced in most of the players, could be accounted for by their higher in vivo susceptibility of LDL to structural modification under conditions of intensive training-induced oxidative stress, despite their apparently normal antioxidant status.

Unrestricted superlensing in a triangular two dimensional photonic crystal

We demonstrate unrestricted superlensing in a triangular twodimensional hotonic crystal. We investigate simple two-point light sources maged by a slab lenses made of this photonic crystal, and show that the efraction of light follows simple rules of geometric optics with the Snell'slaw efraction at each interface, and an effective isotropic refractive index n= -1 for light propagating inside the crystal. We contrast this behavior with that of a square two-dimensional photonic crystal in the first photonic band, where the effective dielectric response is anisotropic. This leads to a restricted superlensing, which does not follow the geometric optics.

Intersubband transport in quantum wells in strong magnetic fields mediated by single- and two-electron scattering

We show theoretically that in quantum wells subjected to a strong magnetic field the intersubband current peaks at magnetic field values, which reveal the underlying specific intersubband scattering mechanism. We have designed and grown a superlattice structure in which such current oscillations are clearly visible, and in which the transition from the purely single-electron to the mixed single- and two-electron scattering regimes can be observed by tuning the applied voltage bias. The measurements were conducted in ultrahigh magnetic fields (up to 45 T) to obtain the full spectrum of the current oscillations.

Resonant tunneling mediated by resonant emission of intersubband plasmons

We study tunneling through resonant tunneling diodes (RTD) with very long emitter drift regions (up to 2 microm). In such diodes, charge accumulation occurs near the double barrier on the emitter side, in a self-induced potential pocket. This leads to a substantial enhancement of the wave function overlap between states of the pocket and the RTD, and, consequently, to increased off-resonant current mediated by various scattering processes. For RTD with the longest drift region (2 microm), an additional strong current peak is observed between the first and the second resonant peaks. We attribute this pronounced feature to the intersubband transitions mediated by resonant emission of intersubband plasmons.

Electromagnetic field strength levels surrounding electronic article surveillance (EAS) systems

Electronic article surveillance (EAS) is used in many applications throughout the world to prevent theft. EAS systems produce electromagnetic (EM) energy around exits to create an EM interrogation zone through which protected items must pass before leaving the establishment. Specially designed EAS tags are attached to these items and must either be deactivated or removed prior to passing through the EAS EM interrogation zone to prevent the alarm from sounding. Recent reports in the scientific literature have noted the possibility that EM energy transmitted by EAS systems may interfere with the proper operation of sensitive electronic medical devices. The Food and Drug Administration has the regulatory responsibility to ensure the safety and effectiveness of medical devices. Because of the possibility of electromagnetic interference (EMI) between EAS systems and electronic medical devices, in situ measurements of the electric and magnetic fields were made around various types of EAS systems. Field strength levels were measured around four types of EAS systems: audio frequency magnetic, pulsed magnetic resonant, radio frequency, and microwave. Field strengths from these EAS systems varied with magnetic fields as high as 1073.6 Am(-1) (in close proximity to the audio frequency magnetic EAS system towers), and electric fields up to 23.8 Vm(-1) (in close proximity to the microwave EAS system towers). Medical devices are only required to withstand 3 Vm(-1) by the International Electrotechnical Commission's current medical device standards. The modulation scheme of the signal transmitted by some types of EAS systems (especially the pulsed magnetic resonant) has been shown to be more likely to cause EMI with electronic medical devices. This study complements other work in the field by attaching specific characteristics to EAS transmitted EM energy. The quantitative data could be used to relate medical device EMI with specific field strength levels and signal waveforms. This is one of several efforts being made by the FDA, the electronic medical device industry and the EAS industry to mitigate the potential for EMI between EAS and medical devices.