Pushing the Limits in Real-Time Measurements of Quantum Dynamics.

Time-resolved studies of quantum systems are the key to understanding quantum dynamics at its core. The real-time measurement of individual quantum numbers as they switch between certain discrete values, well known as a "random telegraph signal," is expected to yield maximal physical insight. However, the signal suffers from both systematic errors, such as a limited time resolution and noise from the measurement apparatus, as well as statistical errors due to a limited amount of data. Here we demonstrate that an evaluation scheme based on factorial cumulants can reduce the influence of such errors by orders of magnitude. The error resilience is supported by a general theory for the detection errors as well as experimental data of single-electron tunneling through a self-assembled quantum dot. Thus, factorial cumulants push the limits in the analysis of random telegraph data, which represent a wide class of experiments in physics, chemistry, engineering, and life sciences.

Optical Detection of Single-Electron Tunneling into a Semiconductor Quantum Dot.

The maximum information of a dynamic quantum system is given by real-time detection of every quantum event, where the ultimate challenge is a stable, sensitive detector with high bandwidth. All physical information can then be drawn from a statistical analysis of the time traces. We demonstrate here an optical detection scheme based on the time-resolved resonance fluorescence on a single quantum dot. Single-electron resolution with high signal-to-noise ratio (4σ confidence) and high bandwidth of 10 kHz make it possible to record the individual quantum events of the transport dynamics. Full counting statistics with factorial cumulants gives access to the nonequilibrium dynamics of spin relaxation of a singly charged dot (γ_{↑↓}=3 ms^{-1}), even in an equilibrium transport measurement.

Cardioprotective effects of low-dose cyclosporin A added to histidine-tryptophan-ketoglutarate cardioplegia solution prior to total myocardial ischemia: an in vitro rabbit heart study.

BACKGROUND/AIMS: Mitochondrial permeability transition pore (MPTP) opening appears to play a key role in myocardial cell survival after ischemia-reperfusion injury and can be inhibited by cyclosporin A (CsA). We investigated whether low-dose CsA added to histidine-tryptophan-ketoglutarate (HTK) cardioplegia solution could improve myocardial protection during longer periods of global myocardial ischemia as encountered during cardiac surgery. METHODS: Rabbit hearts perfused on a Langendorff apparatus were arrested with cold HTK solution containing 1 µmol/l CsA. After 90 min of ischemia, the hearts were reperfused and pmax, max dp/dt, min dp/dt, myocardial stiffness, pO(2), coronary flow and heart rate recorded. Tissue ATP and malondialdehyde (MDA) were measured to assess cell energy content and oxidative stress, respectively. RESULTS: CsA-treated hearts recovered pmax (p = 0.026), max dp/dt (p = 0.028) and min dp/dt (p = 0.025) more quickly and to a greater extent than non-treated hearts. They required markedly less oxygen (p = 0.041) in the first 10 min of reperfusion. Hearts treated with CsA produced 44% less MDA (1.09 vs. 1.93, p = 0.008), while ATP levels were unchanged. CONCLUSIONS: HTK cardioplegia solution containing CsA at a dose well below that expected to cause systemic immunosuppressive effects leads to a significant and timelier recovery of myocardial contractility, while consuming less oxygen.

The activation state of nitrate reductase is not always correlated with total nitrate reductase activity in leaves

The relation between nitrate reductase (NR; EC 1.6.6.1) activity, activation state and NR protein in leaves of barley (Hordeum vulgare L.) seedlings was investigated. Maximum NR activity (NRA(max)) and NR protein content (Western blotting) were modified by growing plants hydroponically at low (0.3 mM) or high (10 mM) nitrate supply. In addition, plants were kept under short-day (8 h light/16 h dark) or long-day (16 h light/8 h dark) conditions in order to manipulate the concentration of nitrate stored in the leaves during the dark phase, and the concentrations of sugars and amino acids accumulated during the light phase, which are potential signalling compounds. Plants were also grown under phosphate deficiency in order to modify their glucose-6-phosphate content. In high-nitrate/long-day conditions, NRA(max) and NR protein were almost constant during the whole light period. Low-nitrate/long-day plants had only about 30% of the NRA(max) and NR protein of high-nitrate plants. In low-nitrate/long-day plants, NRA(max) and NR protein decreased strongly during the second half of the light phase. The decrease was preceded by a strong decrease in the leaf nitrate content. Short daylength generally led to higher nitrate concentrations in leaves. Under short-day/low-nitrate conditions, NRA(max) was slightly higher than under long-day conditions and remained almost constant during the day. This correlated with maintenance of higher nitrate concentrations during the short light period. The NR activation state in the light was very similar in high-nitrate and low-nitrate plants, but dark inactivation was twice as high in the high-nitrate plants. Thus, the low NRA(max) in low-nitrate/long-day plants was slightly compensated by a higher activation state of NR. Such a partial compensation of a low NR(max) by a higher dark activation state was not observed with phosphate-depleted plants. Total leaf concentrations of sugars, of glutamine and glutamate and of glucose-6-phosphate did not correlate with the NR activation state nor with NRA(max).

Intracellular bioaccumulation of zinc by an Enterobacter species.

Bacterial strains tolerant to the presence of 100 mg/l zinc ions were isolated from a water reclamation system. Each of the organisms were screened for their ability to accumulate zinc at the above mentioned concentration. The organism capable of maximum zinc accumulation was identified as an Enterobacter species and intracellular zinc deposition by this micro-organism was determined using energy dispersive X-ray analysis, transmission electron microscopy and a metal-staining technique at the light microscopy level. Further studies revealed that growth and glucose utilization by this isolate were inhibited in the presence of zinc, compared to a control culture grown in the absence of zinc.

Bacterial bioabsorption of nickel from industrial cooling water.

Three bacterial strains tolerant to the presence of 100 mg litre(-1) nickel ions were isolated from a water reclamation system. Each organism was tested for ability to accumulate nickel at the above-mentioned concentration. The organism capable of maximum nickel accumulation was identified as an Enterobacter sp. and intracellular nickel deposition by this microorganism was determined using energy dispersive X-ray analysis (EDAX) and transmission electron microscopy. A metal-staining technique for light microscopy was developed. Further studies revealed that growth and glucose utilisation by this isolate was inhibited in culture by nickel.