Natural Lifetime Research Articles

Ultrafast non-local control of spontaneous emission.

The radiative interaction of solid-state emitters with cavity fields is the basis of semiconductor microcavity lasers and cavity quantum electrodynamics (CQED) systems. Its control in real time would open new avenues for the generation of non-classical light states, the control of entanglement and the modulation of lasers. However, unlike atomic CQED or circuit quantum electrodynamics, the real-time control of radiative processes has not yet been achieved in semiconductors because of the ultrafast timescales involved. Here we propose an ultrafast non-local moulding of the vacuum field in a coupled-cavity system as an approach to the control of radiative processes and demonstrate the dynamic control of the spontaneous emission (SE) of quantum dots (QDs) in a photonic crystal (PhC) cavity on a ∼ 200 ps timescale, much faster than their natural SE lifetimes.

Combined effect of cascade through circular orbits and Stark quenching on the decay of n=2→n=1 transition of H-like Fe in beam–foil excitation

Recently Mishra et al. (Mishra AP, et al. J Quant Spectrosc Radiat Transf 2013;120:114–9), while analyzing the effects of cascading through circular orbits (l=n−1)on the decay of unresolved 2p,2s→1s transitions of H-like Fe, neglected the effect of electric field at the exit surface of foil on the lifetime of the 2s state. In the present work we have considered the combined effect of cascading through circular orbits and the Stark mixing on the decay of the 2p,2s→1s transitions of H-like Fe in beam–foil excitation. It is observed that the natural lifetime of the 2s state (350.6ps) is reduced to 221.8±22.4ps due to Stark mixing of the long-lived 2s2S1/2 state with the very close and short-lived 2pP1/2o2 state. The strength of the electric field responsible for such mixing comes out to be 7.09±0.37×106V/cm. The results of the present work for cascading of circular orbits through the 2p state are in good agreement (within the error bars) with those obtained earlier by Mishra et al.

The electronic spectra of long carbon-chain (13)C2nH/D molecules for ()

Unresolved electronic origin band transitions have been measured for the even-numbered linear carbon-chain radicals (13)C2nH/D with . Spectra of the fully 13C substituted 13C8H/D and 13C10H/D isotopologues are presented for the first time. 12C10H/D and 12C12H/D spectra are presented with improved signal-to-noise ratio to realise a systematic study of the band profiles. Despite the fact that individual rotational transitions cannot be resolved, it is possible to derive effective values for the upper state lifetime. The obtained natural lifetime line broadening parameters of 0.8 ± 0.1 cm−1 for n = 4, 4.0 ± 0.5 cm−1 for n = 5 and 4.8 ± 0.5 cm−1 for n = 6 indicate that internal conversion processes occur in these carbon-chain molecules.

Elements of physics for the 21st century

Given the experimental precision in condensed matter physics – positions are measured with errors of less than 0.1pm, energies with about 0.1meV, and temperature levels are below 20mK – it can be inferred that standard quantum mechanics, with its inherent uncertainties, is a model at the end of its natural lifetime. In this presentation I explore the elements of a future deterministic framework based on the synthesis of wave mechanics and density functional theory at the single-electron level.

Bichromatic resonant light scattering from a quantum dot

We report on resonant light scattering experiments in which a single InAs quantum dot is exposed to two independently tunable continuous-wave lasers while the scattered light is analyzed background free, with high spectral and temporal resolution. In contrast to the well-known monochromatic case exhibiting Rabi oscillations, in this bichromatic case the additional field introduces oscillations at half the difference of the laser frequencies and harmonics thereof, persisting beyond the natural lifetime. The familiar ``dressed-states'' ladder now contains an infinite number of levels per manifold. With suitable averaging, the rich resulting spectra and second-order correlations can be reproduced accurately using the Bloch equations and the quantum regression theorem.

Near infrared luminescent hexanuclear zinc–lanthanide prisms: Synthesis, structure and luminescent properties

The use of the Schiff-base ligand N,N′-bis(3-methoxysalicylidene)ethylene-1,2-diamine (H2L) and fumarate (fum) enables the construction of the hexanuclear luminescent Zn–Ln complexes [Zn4Ln2L4(fum)2] (NO3)2·3CH3OH (Ln=Nd 1; Yb 2; Er 3; Gd 4). The complexes have been characterized by elemental analysis, FT-IR spectra and ESI mass spectrometer. The single crystal X-ray crystallographic study has been carried out on 1. Luminescent properties of these complexes including UV–Vis absorption spectra, excitation, visible and NIR region emission spectra, and NIR emission lifetime have been determined. The intrinsic near-infrared luminescent quantum yield of 1 and 2 are estimated to be 0.63% and 0.84% calculated from the observed lifetime and the natural lifetime of the lanthanide ions, respectively. Systematic analysis suggests that enhancement of near infrared emission could be observed upon construction of the stable polynuclear structures.

Nanosatellite orbit control using MEMS cold gas thrusters

We introduce nanosatellite orbit control using a novel miniaturized cold gas propulsion module based on microelectro- mechanical systems (MEMS) technology. Firstly, the design and characteristics of the propulsion module suitable for CubeSat class nanosatellites are described. Secondly, mission analyses for in-orbit validation of the propulsion module on a 2-unit CubeSat in 300 km low Earth orbit are presented. The MEMS cold gas propulsion module with 10 cm £ 10 cm £ 3 cm dimensions and 220 g mass is specifically designed for use in CubeSats. In baseline configuration with a tank for 60 g of butane under 2 to 5 bar pressure, it can provide up to 15 m/s delta-V capability for a 2.66 kg satellite. The module includes four individually controllable thrusters with proportional thrust regulation and closed loop control; maximum thrust is 1 mN per thruster with 5 N thrust resolution. The fully operational satellite with active orbital control is capable of accommodating a 0.64 kg and 10 cm £ 10 cm £ 7 cm additional payload. The analysed mission scenarios have potential for different Earth observation applications. Natural deorbiting, controlled orbit lowering, controlled orbit raising, and orbit keeping at 300 km altitude are simulated. Simulations indicate that the natural orbit lifetime can be extended from 63 days to 193 days with the baseline propulsion module and satellite altitude can be increased to 348 km or lowered to 257 km. Orbit keeping at 300 km is possible for up to 76 days; proportional thrust control could provide a further increase to 204 days.

Thermal shifts and broadening of Rydberg levels in Be II ions

The effect of a thermal field on Rydberg states of the nS-, nP- and nD-series in beryllium ions Be+ is investigated. The blackbody radiation-induced depopulation rates caused by transitions to upper (excitations) and lower (decays) bound levels and to the continuum (ionization) are calculated in wide ranges of the principal quantum numbers n and ambient temperatures. Simple and reliable approximations for natural lifetimes and stimulated by thermal radiation depopulation rate components are proposed. The blackbody-radiation-induced shifts of Rydberg levels are also calculated and their qualitative and quantitative properties are analysed.

A study of optical properties of Sm3+ ions in α-Na3Y(VO4)2 single crystals

Single crystals of α-Sm3+:Na3Y(VO4)2 have been grown by the flux growth method. The absorption (300K) fluorescence (4.2 and 300K) and excitation (7 and 300K) spectra as well as the fluorescence dynamics of the Sm3+-doped title crystals are presented and analyzed in detail. The energy transfer between Sm3+–Sm3+ as well as from VO43− to Sm3+ were studied in detail. A Judd–Ofelt intensity analysis of the absorption (300K) spectrum has been applied for determination of Ωλ parameters which in turn have been used in calculation of the radiative transition probability factor (A), fluorescence branching ratios (β), natural (radiative) lifetime of the 4G(4)5/2 level of Sm3+ and emission cross-section (σem). For the first time very large lifetimes of the Sm3+ fluorescence level have been observed.

Fluctuated atom-sized junctions in a liquid environment

Durability of atom-sized junctions in a liquid environment was investigated and compared with that in a vacuum. The single atom junction lifetime was measured in an organic solvent under various stretching speed vd ranging from 10 to 0.001 nm/s. We found the natural lifetime of about 1 s for Au single-atom chains formed in a non-polar organic solvent at vd ≤ 0.01 nm/s, which was an order of magnitude shorter than that in a vacuum. The decreased junction lifetime indicates contact instability induced by thermal collisions of solvent molecules that exert pressure on the nanocontacts.

稀土原子与离子的自然辐射寿命测量

稀土原子与离子的自然辐射寿命测量

Theoretical study of potential energy curves, spectroscopic constants, and radiative lifetimes of low-lying states in an SeO molecule

The low-lying potential energy curves of the SeO molecule are computed by means of an ab initio multireference configuration interaction technique, taking into account relativistic (scalar plus spin—orbit coupling) effects. The spectroscopic constants of Ω states for X3Σ−, a1Δ, b1Σ+, A3Π, A′3Δ, and A″ 3Σ+ states are obtained, and they are in good accordance with available experimental values. The Franck—Condon factors and transition dipole moments to the ground state are computed, and the natural radiative lifetimes of low-lying Ω states are theoretically obtained. Comparisons of the natural lifetimes of Ω states with previous experimental results and those of isovalent TeO molecule are made.

Autoionization widths of open-M-shell germanium ions: effects on inner-shell absorptions

Large-scale configuration interaction calculations were carried out to obtain the level-by-level autoionization (AI) rates and resonance widths of the inner-shell excited configurations for the open-M-shell germanium ions. Detailed results are presented for Ge5+ as an example. The dominant ionization channels of the autoionized levels 2p53/23s23p63d10 and 2p51/23s23p63d10 of Ge5+ were determined, and it is shown that the channel from level 3s23p6(3d−13/23d−15/2)4 contributes the largest fraction of AI widths of 0.195 and 0.188 eV to the total width of 0.577 and 0.544 eV, respectively, from all possible channels. For typical experimental plasmas at temperatures of several tens and hundreds of eV, the AI resonance broadening is the dominant mechanism among the Doppler, electron impact and natural lifetime broadenings. Among the physical effects such as relativistic and the interaction between fine-structure levels belonging to the same non-relativistic configuration and different configurations, particular attention is paid to the effect of AI resonance broadening on the L-shell absorption. Different features of the inner-shell absorption due to AI broadening are presented in detail for Ge5+, Ge10+ and Ge17+. The total AI widths of levels from the configuration of one 2p electron being excited to 3d orbital were systematically investigated for Ge6+–Ge21+. Except for Ge20+ and Ge21+, the AI widths of the open-M-shell germanium ions dominate over all other line broadening mechanisms.

Coherent excitation of the 5D5/2 level of ultra-cold rubidium atoms with short laser pulses

We demonstrate the use of stimulated Raman adiabatic passage (STIRAP) for population transfer from the ground state to the 5D5/2 level (5S1/2 → 5P3/2 → 5D5/2) in laser-cooled 87Rb atoms and examine the influence of the time delay between laser pulses, pulse height, pulse duration and frequency detuning from resonance on the efficiency of Rb atom excitation to the 5D5/2 level. In our experiments, the pulse duration was varied widely (30 — 200 ns), which allowed us to assess the effect of spontaneous decay on the population of the 5D5/2 level (natural lifetime, 300 ns). We performed numerical calculations with allowance for spontaneous decay from the 5P3/2 and 5D5/2 levels and compared the results to experimental data, which allowed the population of the 5D5/2 level to be determined. The maximum population of the 5D5/2 level in the region under excitation was 80 % of the total number of rubidium atoms.

Prostate Cancer Screening: What We Know, Don't Know, and Believe

This commentary discusses the U.S. Preventive Services Task Force recommendation against PSA-based screening for men of any age. The commentator agrees with the recommendation and discusses how the...

Longitudinal multistage model for lung cancer incidence, mortality, and CT detected indolent and aggressive cancers

It is currently not known whether most lung cancers detected by computerized tomography (CT) screening are aggressive and likely to be fatal if left untreated, or if a sizable fraction are indolent and unlikely to cause death during the natural lifetime of the individual. We developed a longitudinal biologically-based model of the relationship between individual smoking histories and the probability for lung cancer incidence, CT screen detection, lung cancer mortality, and other-cause mortality. The longitudinal model relates these different outcomes to an underlying lung cancer disease pathway and an effective other-cause mortality pathway, which are both influenced by the individual smoking history. The longitudinal analysis provides additional information over that available if these outcomes were analyzed separately, including testing if the number of CT detected and histologically-confirmed lung cancers is consistent with the expected number of lung cancers “in the pipeline”. We assume indolent nodules undergo Gompertz growth and are detectable by CT, but do not grow large enough to contribute significantly to symptom-based lung cancer incidence or mortality. Likelihood-based model calibration was done jointly to data from 6878 heavy smokers without asbestos exposure in the control (placebo) arm of the Carotene and Retinol Efficacy Trial (CARET); and to 3,642 heavy smokers with comparable smoking histories in the Pittsburgh Lung Screening Study (PLuSS), a single-arm prospective trial of low-dose spiral CT screening for diagnosis of lung cancer. Model calibration was checked using data from two other single-arm prospective CT screening trials, the New York University Lung Cancer Biomarker Center (NYU) (n=1,021), and Moffitt Cancer Center (Moffitt) cohorts (n=677). In the PLuSS cohort, we estimate that at the end of year 2, after the baseline and first annual CT exam, that 33.0 (26.9, 36.9)% of diagnosed lung cancers among females and 7.0 (4.9,11.7)% among males were overdiagnosed due to being indolent cancers. At the end of the PLuSS study, with maximum follow-up of 5.8years, we estimate that due to early detection by CT and limited follow-up, an additional 2.2 (2.0,2.4)% of all diagnosed cancers among females and 7.1 (6.7,8.0)% among males would not have been diagnosed in the absence of CT screening. We also find a higher apparent cure rate for lung cancer among CARET females than males, consistent with the larger indolent fraction of CT detected and histologically confirmed lung cancers among PLuSS females. This suggests that there are significant gender differences in the aggressiveness of lung cancer. Females may have an inherently higher proportion of indolent lung cancers than males, or aggressive lung cancers may be brought into check by the immune system more frequently among females than males.

Lifetimes of Triplet Dissolved Natural Organic Matter (DOM) and the Effect of NaBH4 Reduction on Singlet Oxygen Quantum Yields: Implications for DOM Photophysics

The natural lifetimes of triplet dissolved organic matter ((3)DOM) were determined by an O(2) saturation kinetics study of singlet oxygen quantum yields (Φ(1O2)) in buffered D(2)O. At least two distinct (3)DOM pools are present, and the observed lifetime range (∼20 to 80 μs) leads to a dependence of Φ(1O2) on O(2) concentrations between 29 and 290 μM. Thus, steady-state (1)O(2) concentrations will depend on [O(2)] in natural waters. The lifetimes are essentially identical for DOM samples of different origins and do not vary with excitation wavelength. However, Φ(1O2) varies greatly between samples and decreases with excitation wavelength. These data strongly suggest that (3)DOM quantum yields decrease with excitation wavelength, which gives rise to the Φ(1O2) variation. Borohydride reduction of several samples in both D(2)O and H(2)O lowers the absorbance and (1)O(2) production rates, but it does not alter Φ(1O2). This is consistent with a model in which (1)O(2) sensitizing chromophores are borohydride reducible groups in DOM, such as aromatic ketones. Interpreted in the framework of a charge transfer (CT) model for DOM optical properties, the collective data suggest a model in which electron acceptor moieties are important (1)O(2) sensitizers and where CT interactions of these moieties disrupt their ability to produce (1)O(2).

Resonant charge transfer at dielectric surfaces

We report on the theoretical description of secondary electron emission due to resonant charge transfer occurring during the collision of metastable N2(3Σ+ u ) molecules with dielectric surfaces. The emission is described as a two step process consisting of electron capture to form an intermediate shape resonance N2 -(2Π g ) and subsequent electron emission by decay of this ion, either due to its natural life time or its interaction with the surface. The electron capture is modeled using the Keldysh Green’s function technique and the negative ion decay is described by a combination of the Keldysh technique and a rate equation approach. We find the resonant capture of electrons to be very efficient and the natural decay to be clearly dominating over the surface-induced decay. Secondary electron emission coefficients are calculated for Al2O3, MgO, SiO2, and diamond at several kinetic energies of the projectile. With the exception of MgO the coefficients turn out to be of the order of 10-1 over the whole range of kinetic energies. This rather large value is a direct consequence of the shape resonance acting as a relay state for electron emission.

The essence of yeast quiescence

Like all microorganisms, yeast cells spend most of their natural lifetime in a reversible, quiescent state that is primarily induced by limitation for essential nutrients. Substantial progress has been made in defining the features of quiescent cells and the nutrient-signaling pathways that shape these features. A view that emerges from the wealth of new data is that yeast cells dynamically configure the quiescent state in response to nutritional challenges by using a set of key nutrient-signaling pathways, which (1) regulate pathway-specific effectors, (2) converge on a few regulatory nodes that bundle multiple inputs to communicate unified, graded responses, and (3) mutually modulate their competences to transmit signals. Here, I present an overview of our current understanding of the architecture of these pathways, focusing on how the corresponding core signaling protein kinases (i.e. PKA, TORC1, Snf1, and Pho85) are wired to ensure an adequate response to nutrient starvation, which enables cells to tide over decades, if not centuries, of famine.

High-Accuracy Optical Clock Based on the Octupole Transition inYb+171

We experimentally investigate an optical frequency standard based on the 467 nm (642 THz) electric-octupole reference transition (2)S(1/2)(F=0)→(2)F(7/2)(F=3) in a single trapped (171)Yb(+) ion. The extraordinary features of this transition result from the long natural lifetime and from the 4f(13)6s(2) configuration of the upper state. The electric-quadrupole moment of the (2)F(7/2) state is measured as -0.041(5)ea(0)(2), where e is the elementary charge and a(0) the Bohr radius. We also obtain information on the differential scalar and tensorial components of the static polarizability and of the probe-light-induced ac Stark shift of the octupole transition. With a real-time extrapolation scheme that eliminates this shift, the unperturbed transition frequency is realized with a fractional uncertainty of 7.1×10(-17). The frequency is measured as 642 121 496 772 645.15(52) Hz.