A comparative study of the dosimetric features of α-Al2O3: C, Mg and α-Al2O3: C

A comparative study of the dosimetric features of α-Al2O3:C,Mg and α-Al2O3:C relevant to thermoluminescence dosimetry is reported. A glow curve of α-Al2O3:C,Mg measured at 1°C/s after beta irradiation to 1 Gy shows two subsidiary peaks at 42°C (labelled as I) and 72°C (II) and the main peak at 161°C (III) whereas a glow curve of α-Al2O3:C measured under the same conditions shows the main peak at 178°C (II′) and a lower intensity peak at 48°C (I′). Apart from these ones, there are several other peaks at temperatures beyond that of the main peak in both α-Al2O3:C,Mg and α-Al2O3:C. However, the latter are not included in this study. We report a comparative quantitative analysis of dose response and fading of peaks I, II and III of α-Al2O3:C,Mg and peaks I′ and II′ of α-Al2O3:C. Analysis shows that the dose response of peaks I and III is sublinear within 1–10 Gy whereas that of peak II is superlinear within 1–4 Gy followed by a sublinear region within 4–10 Gy. In comparison, the dose response of peak I′ is superlinear within 1–4 Gy followed by a sublinear region within 4–10 Gy whereas that of peak II′ is sublinear within 1–4 Gy followed by a superlinear region within 4–10 Gy. As regards to fading corresponding to 1 Gy, peak I is very unstable and fades within 300 s, peak II is more stable and takes up to 43200 s to fade. In comparison, peak III fades down to 30% of its initial intensity within 2400 s. Interestingly, between 2400 and 800 s, the intensity fades by 17% only. Regarding fading in α-Al2O3:C, peak I′ fades within 600 s whereas peak II′ shows an inverse fading behaviour up to 64800 s. The rate of fading for peaks I, II and III in α-Al2O3:C,Mg was found to decrease with increase in dose. However, no such behaviour was observed in α-Al2O3:C. The fading in both samples is discussed on the basis of a charge hopping mechanism

Single track coincidence measurements of fluorescent and plastic nuclear track detectors in therapeutic carbon beams

In this paper we present a method for single track coincidence measurements using two different track detector materials. We employed plastic and fluorescent nuclear track detectors (PNTDs and FNTDs) in the entrance channel of a monoenergetic carbon ion beam covering the therapeutically useful energy range from 80 to 425 MeV/u. About 99 % of all primary particle tracks detected by both detectors were successfully matched, while 1 % of the particles were only detected by the FNTDs because of their superior spatial resolution. We conclude that both PNTDs and FNTDs are suitable for clinical carbon beam dosimetry with a detection efficiency of at least 98.82 % and 99.83 % respectively, if irradiations are performed with low fluence in the entrance channel of the ion beam. The investigated method can be adapted to other nuclear track detectors and offers the possibility to characterize new track detector materials against well-known detectors. Further, by combining two detectors with a restricted working range in the presented way a hybrid-detector system can be created with an extended and optimized working range.Comment: 14 pages, 8 figures, 2 table

Cryogenic Ion Trapping Systems with Surface-Electrode Traps

We present two simple cryogenic RF ion trap systems in which cryogenic temperatures and ultra high vacuum pressures can be reached in as little as 12 hours. The ion traps are operated either in a liquid helium bath cryostat or in a low vibration closed cycle cryostat. The fast turn around time and availability of buffer gas cooling made the systems ideal for testing surface-electrode ion traps. The vibration amplitude of the closed cycled cryostat was found to be below 106 nm. We evaluated the systems by loading surface-electrode ion traps with $^{88}$Sr$^+$ ions using laser ablation, which is compatible with the cryogenic environment. Using Doppler cooling we observed small ion crystals in which optically resolved ions have a trapped lifetime over 2500 minutes.Comment: 10 pages, 13 EPS figure

Efficient Nanosecond Photoluminescence from Infrared PbS Quantum Dots Coupled to Plasmonic Nanoantennas

Infrared (IR) light sources with high modulation rates are critical components for on-chip optical communications. Lead-based colloidal quantum dots are promising nonepitaxial materials for use in IR light-emitting diodes, but their slow photoluminescence lifetime is a serious limitation. Here we demonstrate coupling of PbS quantum dots to colloidal plasmonic nanoantennas based on film-coupled metal nanocubes, resulting in a dramatic 1300-fold reduction in the emission lifetime from the microsecond to the nanosecond regime. This lifetime reduction is primarily due to a 1100-fold increase in the radiative decay rate owing to the high quantum yield (65%) of the antenna. The short emission lifetime is accompanied by high antenna quantum efficiency and directionality. This nonepitaxial platform points toward GHz frequency, electrically modulated, telecommunication wavelength light-emitting diodes and single-photon sources.United States. Dept. of Energy. Center for Excitonics (Award DE-SC0001088

Trion induced negative photoconductivity in monolayer MoS2

Optical excitation typically enhances electrical conduction and low-frequency radiation absorption in semiconductors. We have, however, observed a pronounced transient decrease of conductivity in doped monolayer molybdenum disulfide (MoS2), a two-dimensional (2D) semiconductor, under femtosecond laser excitation. In particular, the conductivity is reduced dramatically down to only 30% of its equilibrium value with high pump fluence. This anomalous phenomenon arises from the strong many-body interactions in the system, where photoexcited electron-hole pairs join the doping-induced charges to form trions, bound states of two electrons and one hole. The resultant increase of the carrier effective mass substantially diminishes the carrier conductivity

Validity of the Polar V800 heart rate monitor to measure RR intervals at rest

Purpose To assess the validity of RR intervals and short-term heart rate variability (HRV) data obtained from the Polar V800 heart rate monitor, in comparison to an electrocardiograph (ECG). Method Twenty participants completed an active orthostatic test using the V800 and ECG. An improved method for the identification and correction of RR intervals was employed prior to HRV analysis. Agreement of the data was assessed using intra-class correlation coefficients (ICC), Bland–Altman limits of agreement (LoA), and effect size (ES). Results A small number of errors were detected between ECG and Polar RR signal, with a combined error rate of 0.086 %. The RR intervals from ECG to V800 were significantly different, but with small ES for both supine corrected and standing corrected data (ES 0.999 for both supine and standing corrected intervals. When analysed with the same HRV software no significant differences were observed in any HRV parameters, for either supine or standing; the data displayed small bias and tight LoA, strong ICC (>0.99) and small ES (≤0.029). Conclusions The V800 improves over previous Polar models, with narrower LoA, stronger ICC and smaller ES for both the RR intervals and HRV parameters. The findings support the validity of the Polar V800 and its ability to produce RR interval recordings consistent with an ECG. In addition, HRV parameters derived from these recordings are also highly comparable

Leveraging Nanocavity Harmonics for Control of Optical Processes in 2D Semiconductors

Optical cavities with multiple tunable resonances have the potential to provide unique electromagnetic environments at two or more distinct wavelengths—critical for control of optical processes such as nonlinear generation, entangled photon generation, or photoluminescence (PL) enhancement. Here, we show a plasmonic nanocavity based on a nanopatch antenna design that has two tunable resonant modes in the visible spectrum separated by 350 nm and with line widths of ∼60 nm. The importance of utilizing two resonances simultaneously is demonstrated by integrating monolayer MoS[subscript 2], a two-dimensional semiconductor, into the colloidally synthesized nanocavities. We observe a 2000-fold enhancement in the PL intensity of MoS[subscript 2]—which has intrinsically low absorption and small quantum yield—at room temperature, enabled by the combination of tailored absorption enhancement at the first harmonic and PL quantum-yield enhancement at the fundamental resonance.United States. Dept. of Energy. Center for Excitonics (Award DE-SC0001088)United States. Dept. of Energy. Office of Basic Energy Sciences (Grant DE-SC0001088

Cardiorespiratory synchronization: is it a real phenomenon

Abstract In this work we present a quantitative approach to the analysis of cardiorespiratory synchronization, which is a newly discovered phenomenon. The primary aim of this Introduction Modulation of heart rate (HR) by respiration, which is the main source of heart rate variability, is long known. This phenomenon has been studied extensively, and although it is not fully understood, its physiological determinants have been unveiled. Lately, the study of phase synchronization in chaotic oscillators has led to the discovery of another aspect of cardiorespiratory interaction: synchronization between respiration and HR [I]. Cardiorespiratory synchronization (CS) was observed in young athletes in coexistence with modulation of HR by respiration. The synchronization was found using a novel visualization tool, the Synchrogram [ 11. The Synchrogram enables to visually detect epochs of synchrony between two noisy signals, with any rational frequency ratio. The qualitative analysis of cardiorespiratory interaction presented in [1,2] raises two questions: a) is cardiorespiratory synchronization a real phenomenon, The two questions are related. Associating distinct physiological conditions to CS negates the hypothesis of CS being random. Indeed, preliminary results indicate that CS is associated with lower HR variability, and more specifically, with reduced values of parasympathetic activity [l-21. In this work, we apply the approach of surrogate data analysis to the study of CS, in order to answer the first question. Surrogate data 'analysis is a widely used approach in the field of nonlinear dynamics, especially when trying to assess a functional relation between an attribute of a system to one of its features. The essence of surrogate analysis is the construction of a (surrogate) data set from the original data, while preserving all features of the data, except for the one whose influence is being tested. A difference in the measured attribute between the real and surrogate data then indicates that it is related to that specific feature that is absent in the surrogates. Our analysis relates the heart-respiration coupling to the synchronization between them. The surrogates were constructed by considering the interaction between respiration and heart rate taken from different subjects. Avoiding randomization of the signals themselves, as commonly done in surrogate data analysis, preserves all features of the cardiorespiratory system, except for the coupling between the two subsystems. We applied a previously developed algorithm, which enables to quantify CS [3], to the analysis of the real and surrogate data. We then compared the statistical properties of the observed CS in both real and surrogate data. Our results show that synchronization appears in both real and surrogate data, although significantly less in the surrogates. Cardiorespiratory synchronization should therefore enter the cadre of cardiorespiratory interactions. Unveiling its physiological determinants and relating cardiorespiratory pathologies to CS will undoubtedly increase our knowledge of this complex system

Multifractality in Human Heartbeat Dynamics

Recent evidence suggests that physiological signals under healthy conditions may have a fractal temporal structure. We investigate the possibility that time series generated by certain physiological control systems may be members of a special class of complex processes, termed multifractal, which require a large number of exponents to characterize their scaling properties. We report on evidence for multifractality in a biological dynamical system --- the healthy human heartbeat. Further, we show that the multifractal character and nonlinear properties of the healthy heart rate are encoded in the Fourier phases. We uncover a loss of multifractality for a life-threatening condition, congestive heart failure.Comment: 19 pages, latex2e using rotate and epsf, with 5 ps figures; to appear in Nature, 3 June, 199