Metal doped polyaniline as neuromorphic circuit elements for in-materia computing.

Polyaniline-based atomic switches are material building blocks whose nanoscale structure and resultant neuromorphic character provide a new physical substrate for the development next-generation, nanoarchitectonic-enabled computing systems. Metal ion-doped devices consisting of a Ag/metal ion doped polyaniline/Pt sandwich structure were fabricated using an in situ wet process. The devices exhibited repeatable resistive switching between high (ON) and low (OFF) conductance states in both Ag+ and Cu2+ ion-doped devices. The threshold voltage for switching was>0.8 V and average ON/OFF conductance ratios (30 cycles for 3 samples) were 13 and 16 for Ag+ and Cu2+ devices, respectively. The ON state duration was determined by the decay to an OFF state after pulsed voltages of differing amplitude and frequency. The switching behaviour is analagous to short-term (STM) and long-term (LTM) memories of biological synapses. Memristive behaviour and evidence of quantized conductance were also observed and interpreted in terms of metal filament formation bridging the metal doped polymer layer. The successful realization of these properties within physical material systems indicate polyaniline frameworks as suitable neuromorphic substrates for in materia computing.

Investigation of Ag and Cu Filament Formation Inside the Metal Sulfide Layer of an Atomic Switch Based on Point-Contact Spectroscopy.

The atomic switches have attracted wide attention owing to their applications in nonvolatile electric devices. The atomic switch is operated by the formation and dissipation of a metallic filament inside a metal sulfide film, which is controlled by a solid electrochemical reaction. Although the metallic filament is considered to consist of metal atoms, the chemical species of the metallic filament are difficult to be identified due to challenges in observing the metallic filament inside the solid. In this study, we report the investigation on the metallic filament in the atomic switch with metal sulfide based on point-contact spectroscopy (PCS). By cooling the atomic switch, the switch voltage increased to 1 V, which allowed for the PCS measurement. The PCS revealed that the metallic filament was composed of Ag atoms in the case of the Pt/Ag2S/Ag atomic switch. We applied this technique to the Pt/Cu2S/Ag and Pt/Ag2S/Cu atomic switches to uncover the formation process of the metallic filament. In both atomic switches, the chemical species of the metallic filament were Ag. The metal atoms were supplied from both the metal electrode and the sulfide layer.

Volatile and nonvolatile selective switching of a photo-assisted initialized atomic switch.

A photo-assisted atomic switch, which has a photoconductive molecular layer in a gap of about 20 nm between an Ag2S electrode and a Pt electrode, is set to a conventional gap-type atomic switch operation mode by light irradiation with the application of a small bias that precipitates Ag atoms from an Ag2S electrode. After this initialization, the switch operates only with application of a bias. In this study, we also found that after the set-operation a photo-assisted initialized atomic switch shows different switching modes depending on the bias range, i.e., volatile switching when the applied bias is smaller than the threshold bias, and nonvolatile switching when the applied bias is larger than the threshold bias. These characteristics can be useful in reconfiguring a circuit such as in neural computing systems.

Forming and switching mechanisms of a cation-migration-based oxide resistive memory.

We report detailed current-voltage and current-time measurements to reveal the forming and switching behaviors of Cu/Ta(2)O(5)/Pt nonvolatile resistive memory devices. The devices can be initially SET (from the OFF state to the ON state) when a low positive bias voltage is applied to the Cu electrode. This first SET operation corresponds to the first formation of a metal filament by inhomogeneous nucleation and subsequent growth of Cu on the Pt electrode, based on the migration of Cu ions in the stable Ta(2)O(5) matrix. After the forming, the device exhibits bipolar switching behavior (SET at positive bias and RESET (from the ON state to the OFF state) at negative bias) with increasing the ON resistance from a few hundred Ω to a few kΩ. From the measurements of the temperature stability of the ON states, we concluded that the RESET process consists of the Joule-heating-assisted oxidation of Cu atoms at the thinnest part of the metal filament followed by diffusion and drift of the Cu ions under their own concentration gradient and the applied electric field, disconnecting the metal filament. With ON resistances of the order of a few kΩ, the SET and RESET operations are repeated by the inhomogeneous nucleation and the Joule-heating-assisted dissolution of a small filament on a remaining filament. This switching model is applicable to the operation of cation-migration-based resistive memories using other oxide materials.

Usefulness of (123)I-BMIPP with myocardial imaging for evaluation of the efficacy of drug therapy in patients with chronic heart failure.

BACKGROUND: Fatty acid is a main source of cardiac energy in aerobic conditions. We used iodine-123-beta-methyl-iodophenyl pentadecanoic acid ((123)I-BMIPP) myocardial scintigraphy to study the efficacy of the angiotensin-converting enzyme inhibitor (ACEI) enalapril in the treatment of chronic heart failure (CHF) by evaluating its therapeutic effects on myocardial fatty acid metabolism. METHODS AND RESULTS: New York Heart Association functional class status, left ventricular end-diastolic diameter, percent fractional shortening, the ratio between early and late peaks of flow velocity, (123)I-BMIPP myocardial-to-mediastinal uptake ratio, and mean washout rate were measured in 42 patients (31 men and 11 women; mean age, 58 +/- 3 years) with CHF before treatment and 3 months after treatment. There was a significant correlation between myocardial fatty acid metabolism and other variables as well as between the degree of improvement in myocardial fatty acid metabolism and the degree of improvement in other variables. CONCLUSIONS: Enalapril improved symptoms and cardiac function in patients with CHF. These improvements significantly correlated with improvement of (123)I-BMIPP metabolism in the myocardium. (123)I-BMIPP scintigraphy is useful for evaluating the efficacy of drug therapy for CHF based on myocardial fatty acid metabolism.

Effect of sealing and Tween 80 on the antifungal susceptibility testing of essential oils.

Concentrations of essential oils showing high volatility decreased substantially in broth and agar media when incubated under open conditions. The decrease in the half life was from 0.7 to 38 hr in broth medium at 27 C. When evaporation was prevented by sealing, MIC values against Aspergillus fumigatus, Candida albicans and Trichophyton mentagrophytes by broth or agar dilution assay were lowered two to eight-fold, as compared with those obtained under open conditions. Addition of Tween 80 caused a rise of the MICs against A. fumigatus by two to four-fold in broth dilution assay, but little affected the MICs in agar dilution assay.

Subacute and chronic effects of DDD pacing on left ventricular diastolic function in patients with non-obstructive hypertrophic cardiomyopathy.

The present study examined the ability of dual-chamber (DDD) pacing to improve symptoms and exercise tolerance in patients with non-obstructive hypertrophic cardiomyopathy (HNCM). Seven patients with HNCM who had failed to benefit from pharmacotherapy participated in the study. The New York Heart Association (NHYA) functional class status and exercise tolerance, which was determined by the treadmill exercise test, were recorded and an echocardiographic observation was performed before, and 1 week, 3 months and 1 year after the implantation of a permanent DDD pacemaker. The atrioventricular delay (AVd) was determined by measuring the point of peak rapid filling velocity and maximum cardiac output (CO). Two patients were not implanted with a permanent pacemaker because their CO and blood pressure decreased or because palpitation occurred during temporary pacing. The ratio between early and late peaks of flow velocity (1.56, 1.21,0.95, and 0.86 before implantation and 1 week, 3 months and 1 year after implantation, respectively); deceleration time (ms: 263.2, 217.6, 204.6, 187.0); peak filling rate (ml/s: 146.2, 204.0, 233.2, 243.6); NYHA functional class status (2.0, 1.8, 1.6, 1.4); and exercise tolerance (s: 203, 264, 403, 480) were significantly improved after implantation. However, left ventricular dimension, percent fractional shortening, ejection fraction, acceleration time and the isovolumic relaxation time were not changed significantly. In conclusion, DDD pacing improved symptoms and the NYHA functional class status, which is associated with improvement of left ventricular diastolic function. It is proposed that DDD pacing would be useful in patients not only with obstructive but also non-obstructive hypertrophic cardiomyopathy refractory to medical treatment, depending on the careful selection of subjects.

[Effects of cilostazol in patients with bradycardiac atrial fibrillation].

OBJECTIVES: Cilostazol, an antithrombotic agent, directly and indirectly increases the heart rate. This study investigated whether cilostazol increases the heart rate, and whether it has chronotropic effects on cardiac failure in patients with bradycardiac atrial fibrillation. METHODS: Twelve patients (6 males and 6 females) with bradycardiac atrial fibrillation underwent Holter monitoring (24-hour total heartbeat counts and frequency of pause), echocardiography (left ventricular end-diastolic diameter, percentage fractional shortening), chest roentgenography (cardiothoracic ratio), and measurements of brain natriuretic peptide and atrial natriuretic peptide before and 6 months after daily oral administration of 100-200 mg cilostazol. RESULTS: Cilostazol administration increased the 24-hour total heartbeat counts from 69,685 +/- 1,690 (mean +/- SE; mean heart rate: 48 beats/min) to 87,352 +/- 3,123 (60), and decreased the frequency of pause from 362.3 +/- 72.9 to 112.3 +/- 41.0. Cardiothoracic ratio decreased from 55.8 +/- 1.1% to 52.5 +/- 1.1%, left ventricular end-diastolic diameter from 56.1 +/- 0.9 to 52.9 +/- 0.8 mm, but percentage fractional shortening was not significantly changed (from 33.0 +/- 2.2% to 33.7 +/- 2.1%). Brain natriuretic peptide decreased from 97.9 +/- 20.5 to 33.5 +/- 4.8 pg/ml, and atrial natriuretic peptide from 69.5 +/- 12.1 to 46.7 +/- 8.3 pg/ml. CONCLUSIONS: Cilostazol has beneficial effects in patients with bradycardiac atrial fibrillation. The increase of heart rate may be mediated by improvement of conductivity in the atrioventricular node and increase of coronary blood supply caused by dilation of vessels.

Major complications during spasm provocation tests with an intracoronary injection of acetylcholine.

This study sought to clarify major complications associated with acetylcholine testing. Serious major complications, such as sustained ventricular tachycardia, shock, and cardiac tamponade were determined in 4 of 715 patients (0.56%), but no cases of death or irreversible complications occurred. The spasm provocation test using acetylcholine should be performed carefully, although it is considered a safe and reliable method.

[Usefulness of washout rate analysis in adenosine triphosphate-stress thallium-201 myocardial scintigraphy in patients with vasospastic angina].

OBJECTIVES: This study evaluated the usefulness of washout rate analysis in adenosine triphosphate(ATP) stress thallium-201 scintigraphy for the diagnosis of vasospastic angina. METHODS: This study included 76 patients with vasospastic angina and 18 normal controls undergoing coronary arteriography. If significant coronary artery stenosis (> or = 50%) was pointed out, the subject was excluded from this study. 111 MBq of thallium-201 was intravenously injected 3 min after ATP loading (0.16 mg/kg/min) was started. Single photon emission computed tomography (SPECT) was performed 10 min and 4 hr after intravenous injection of ATP. The mean washout rate (%) was calculated based on a bull's eye map and was divided into 3 regions, the antero-septal/lateral/inferior regions. The washout rate in each region was calculated. Regional uptake was visually estimated based on the 17 segments of SPECT images. RESULTS: The washout rate in the normal control group was 48.9 +/- 4.1 (mean +/- SD)%. In patients with vasospastic angina, the washout rate in areas with coronary vasospasm was 33.4 +/- 5.5%. This value was significantly lower than in the areas without coronary vasospasm (42.8 +/- 3.6%). The usefulness of washout rate analysis in the diagnosis of vasospastic angina with a cut-off value of less than -2SD from normal washout rate in the 3 regions was examined. A significantly higher diagnostic value was found by washout rate analysis (sensitivity 72.3%, specificity 79.7%, and accuracy 74.6%) compared with visual evaluation of early images (sensitivity 50.3%, specificity 73.9%, and accuracy 57.5%). CONCLUSIONS: The diagnostic value of washout rate analysis was significantly higher (73.1%) compared with visual evaluation of early images (50.3%) in patients with multivessel vasospastic angina.