Quantum light emission of two lateral tunnel-coupled (In,Ga)As/GaAs quantum dots controlled by a tunable static electric field

Lateral quantum coupling between two self-assembled (In,Ga)As quantum dots has been observed. Photon statistics measurements between the various excitonic and biexcitonic transitions of these lateral quantum dot molecules display strong antibunching confirming the presence of coupling. Furthermore, we observe an anomalous exciton Stark shift with respect to static electric field. A simple model indicates that the lateral coupling is due to electron tunneling between the dots when the ground states are in resonance. The electron probability can then be shifted to either dot and the system can be used to create a wavelength-tunable single-photon emitter by simply applying a voltage.     

Energy spectra for decaying 2D turbulence in a bounded domain

We use results derived in the framework of the replica approach to study the liquid-glass thermodynamic transition. The main results are derived without using replicas and applied to the study of the Lennard-Jones binary mixture introduced by Kob and Andersen. We find that there is a phase transition due to the entropy crisis. We compute both analytically and numerically the value of the phase transition point T(K) and the specific heat in the low temperature phase.     

Development and qualification of a size exclusion chromatography coupled with multiangle light scattering method for molecular weight determination of unfractionated heparin

The molecular weight of unfractionated heparin was determined by size exclusion chromatography (SEC) coupled with multiangle light scattering (MALS) detection. The SEC/MALS method determines absolute molecular weight directly from the angular dependence of scattered light intensity as a function of concentration and does not rely on molecular weight standards for column calibration. The SEC/MALS method developed at Scientific Protein Laboratories was qualified in terms of specificity, precision, robustness, and accuracy. By eliminating the requirement of well-characterized molecular weight standards derived from heparin, the present procedure represents a clear improvement over the column calibration methods used in molecular weight determination. The SEC/MALS method is suitable for routine quality control of unfractionated heparin.     

3D printed titanium micro-bore columns containing polymer monoliths for reversed-phase liquid chromatography

The potential of 3D selective laser melting (SLM) technology to produce compact, temperature and pressure stable titanium alloy chromatographic columns is explored. A micro bore channel (0.9 mm I.D. × 600 mm long) was produced within a 5 × 30 × 30 mm titanium alloy (Ti–6Al–4V) cuboid, in form of a double handed spiral. A poly(butyl methacrylate-co-ethyleneglycoldimethacrylate) (BuMA-co-EDMA) monolithic stationary phase was thermally polymerised within the channel for application in reversed-phase high-performance liquid chromatography. The prepared monolithic column was applied to the liquid chromatographic separation of intact proteins and peptides. Peak capacities of 69–76 (for 6–8 proteins respectively) were observed during isothermal separation of proteins at 44 °C which were further increased to 73–77 using a thermal step gradient with programmed temperature from 60 °C to 35 °C using an in-house built direct-contact heater/cooler platform based upon matching sized Peltier thermoelectric modules. Rapid temperature gradients were possible due to direct-contact between the planar metal column and the Peltier module, and the high thermal conductivity of the titanium column as compared to a similar stainless steel printed column. The separation of peptides released from a digestion of E.coli was also achieved in less than 35 min with ca. 40 distinguishable peaks at 210 nm.     

Influence of the dark exciton state on the optical and quantum optical properties of single quantum dots

The dark exciton state strongly affects the optical and quantum optical properties of flat InP/GaInP quantum dots. The exciton intensity drops sharply compared to the biexciton with rising pulsed laser excitation power while the opposite is true with temperature. Also, the decay rate is faster for the exciton than the biexciton and the dark-to-bright state spin flip is enhanced with temperature. Furthermore, long-lived dark state related memory effects are observed in second-order cross-correlation measurements between the exciton and biexciton and have been simulated using a rate-equation model.     

Alkylation of the chrysin dianion

Alkylation of the disodium salt of chrysin in liquid ammonia with methyl iodide gave a mixture of the 6-and 8-monomethyl derivatives, while with prenyl bromide the 6-mono- and the 6,8-diprenyl derivatives were obtained. Nuclear methylation was also achieved by means of dimethyl sulphate. With benzyl chloride as alkylating agent benzylation did not occur under similar conditions, but the 6-C, 7-O-dibenzyl derivative was obtained when the liquid ammonia was replaced by dioxan.     

Red Light Treatment in an Axotomy Model of Neurodegeneration

Red light has been shown to provide neuroprotective effects. Axotomizing the optic nerve initiates retinal ganglion cell (RGC) degeneration, and an early marker of this is dendritic pruning. We hypothesized that 670 nm light can delay axotomy‐induced dendritic pruning in the retinal explant. To test this hypothesis, we monitored the effects of 670 nm light (radiant exposure of 31.7 J cm^?2), on RGC dendritic pruning in retinal explants from C57BL/6J mice, at 40 min, 8 h and 16 h post axotomy. For sham‐treated retinae, area under the Sholl curve, peak of the Sholl curve and dendritic length at 8 h post axotomy showed statistically significant reductions by 42.3% (P = 0.008), 29.8% (P = 0.007) and 38.4% (P = 0.038), respectively, which were further reduced after 16 h by 40.56% (P < 0.008), 33.9% (P < 0.007), 45.43% (P < 0.006), respectively. Dendritic field area was also significantly reduced after 16 h, by 44.23% (P < 0.019). Such statistically significant reductions were not seen in light‐treated RGCs at 8 or 16 h post axotomy. The results demonstrate the ability of 670 nm light to partially prevent ex vivo dendropathy in the mouse retina, suggesting that it is worth exploring as a treatment option for dendropathy‐associated neurodegenerative diseases, including glaucoma and Alzheimer's disease.     

Electrochemical processes in electrospray ionization mass spectrometry

Editorial Comment Last month we presented, as a Special Feature, a set of five articles that constituted a Commentary on the fundamentals and mechanism of electrospray ionization (ESI). These articles produced some lively discussion among the authors on the role of electrochemistry in ESI. Six authors participated in a detailed exchange of views on this topic, the final results of which constitute this month's Special Feature. We particularly hope that younger scientists will find value in this month's Special Feature, not only for the science that it teaches but also what it reveals about the processes by which scientific conclusions are drawn. To a degree, the contributions part the curtains on these processes and show science in action. We sincerely thank the contributors to this discussion. The give and take of intellectual debate is not always easy, and to a remarkable extent this set of authors has maintained good humor and friendships, even when disagreeing strongly on substance. Graham Cooks and Richard Caprioli Copyright 2000 John Wiley & Sons, Ltd.     

Derivatization for electrospray ionization-mass spectrometry. 4. Alkenes and alkynes

A survey of derivatization strategies and prospective derivatization reactions for conversion of simple alkenes and alkynes to 'electrospray-active' species is presented. General synthetic strategies are discussed and illustrative examples of prospective derivatives prepared from model compounds are presented along with their electrospray ionization (ES) mass spectra. The identified derivatives of these neutral, nonpolar analytes are either ionic or are ionizable in solution through Bronsted acid/base chemistry, by Lewis acid/base chemistry, or by chemical or electrochemical electron-transfer chemistry. Once ionized, the derivatives are expected to be amenable to detection by electrospray ionization-mass spectrometry. Derivatives are identified for positive and negative ion analysis of both alkenes and alkynes. Copyright 2000 John Wiley & Sons, Ltd.