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This review analyzes the causes and consequences of apoptosis resulting from oxidative stress that occurs in mitochondria and cells exposed to the toxic effects of different-valence heavy metals (Ag+, Tl+, Hg2+, Cd2+, Pb2+, Al3+, Ga3+, In3+, As3+, Sb3+, Cr6+, and U6+). The problems of the relationship between the integration of these toxic metals into molecular mechanisms with the subsequent development of pathophysiological processes and the appearance of diseases caused by the accumulation of these metals in the body are also addressed in this review. Such apoptosis is characterized by a reduction in cell viability, the activation of caspase-3 and caspase-9, the expression of pro-apoptotic genes (Bax and Bcl-2), and the activation of protein kinases (ERK, JNK, p53, and p38) by mitogens. Moreover, the oxidative stress manifests as the mitochondrial permeability transition pore (MPTP) opening, mitochondrial swelling, an increase in the production of reactive oxygen species (ROS) and H2O2, lipid peroxidation, cytochrome c release, a decline in the inner mitochondrial membrane potential (ΔΨmito), a decrease in ATP synthesis, and reduced glutathione and oxygen consumption as well as cytoplasm and matrix calcium overload due to Ca2+ release from the endoplasmic reticulum (ER). The apoptosis and respiratory dysfunction induced by these metals are discussed regarding their interaction with cellular and mitochondrial thiol groups and Fe2+ metabolism disturbance. Similarities and differences in the toxic effects of Tl+ from those of other heavy metals under review are discussed. Similarities may be due to the increase in the cytoplasmic calcium concentration induced by Tl+ and these metals. One difference discussed is the failure to decrease Tl+ toxicity through metallothionein-dependent mechanisms. Another difference could be the decrease in reduced glutathione in the matrix due to the reversible oxidation of Tl+ to Tl3+ near the centers of ROS generation in the respiratory chain. The latter may explain why thallium toxicity to humans turned out to be higher than the toxicity of mercury, lead, cadmium, copper, and zinc.

Real-time quantum feedback based on weak measurement of the quantum state is used to stabilize the oscillation phase of a driven quantum bit. Winding the quantum clock By performing weak measurements of a quantum state, it is possible to slow the rate of collapse of its wavefunction, so that information about the quantum state can be gradually acquired. Such information can be used to continuously track and steer the quantum state using feedback. This paper reports quantum feedback control of a superconducting quantum bit (qubit) coupled to a microwave cavity. The qubit undergoes coherent oscillations that can be made to speed up, slow down or persist indefinitely. This ability to actively suppress decoherence could find many applications in quantum error correction, quantum-state stabilization and purification, entanglement generation and adaptive measurements. The act of measurement bridges the quantum and classical worlds by projecting a superposition of possible states into a single (probabilistic) outcome. The timescale of this ‘instantaneous’ process can be stretched using weak measurements 1 , 2 , such that it takes the form of a gradual random walk towards a final state. Remarkably, the interim measurement record is sufficient to continuously track and steer the quantum state using feedback 3 , 4 , 5 , 6 , 7 , 8 . Here we implement quantum feedback control in a solid-state system, namely a superconducting quantum bit (qubit) coupled to a microwave cavity 9 . A weak measurement of the qubit is implemented by probing the cavity with microwave photons, maintaining its average occupation at less than one photon. These photons are then directed to a high-bandwidth, quantum-noise-limited amplifier 10 , 11 , which allows real-time monitoring of the state of the cavity (and, hence, that of the qubit) with high fidelity. We demonstrate quantum feedback control by inhibiting the decay of Rabi oscillations, allowing them to persist indefinitely 12 . Such an ability permits the active suppression of decoherence and enables a method of quantum error correction based on weak continuous measurements 13 , 14 . Other applications include quantum state stabilization 4 , 7 , 15 , entanglement generation using measurement 16 , state purification 17 and adaptive measurements 18 , 19 .

A universal set of logic gates in a superconducting quantum circuit is shown to have gate fidelities at the threshold for fault-tolerant quantum computing by the surface code approach, in which the quantum bits are distributed in an array of planar topology and have only nearest-neighbour couplings. Error-free quantum computing in prospect Quantum computers can only work in practice if, like conventional computers, they are fault-tolerant. This means that a system has to be in place to detect any errors and correct them. For quantum error correction such a system involves entangling several quantum bits (qubits) with each other. In the so-called surface code error-correction architecture, qubits are placed in a lattice and are entangled with four nearest neighbours. Rami Barends et al . report the construction of such a surface code system with five qubits in a row made from superconducting devices. This system performs with fidelity that is at the threshold for quantum error correction, suggesting that error-free quantum computing should be possible. The platform lends itself to scaling up to larger numbers of qubits and two-dimensional architecture. A quantum computer can solve hard problems, such as prime factoring 1 , 2 , database searching 3 , 4 and quantum simulation 5 , at the cost of needing to protect fragile quantum states from error. Quantum error correction 6 provides this protection by distributing a logical state among many physical quantum bits (qubits) by means of quantum entanglement. Superconductivity is a useful phenomenon in this regard, because it allows the construction of large quantum circuits and is compatible with microfabrication. For superconducting qubits, the surface code approach to quantum computing 7 is a natural choice for error correction, because it uses only nearest-neighbour coupling and rapidly cycled entangling gates. The gate fidelity requirements are modest: the per-step fidelity threshold is only about 99 per cent. Here we demonstrate a universal set of logic gates in a superconducting multi-qubit processor, achieving an average single-qubit gate fidelity of 99.92 per cent and a two-qubit gate fidelity of up to 99.4 per cent. This places Josephson quantum computing at the fault-tolerance threshold for surface code error correction. Our quantum processor is a first step towards the surface code, using five qubits arranged in a linear array with nearest-neighbour coupling. As a further demonstration, we construct a five-qubit Greenberger–Horne–Zeilinger state 8 , 9 using the complete circuit and full set of gates. The results demonstrate that Josephson quantum computing is a high-fidelity technology, with a clear path to scaling up to large-scale, fault-tolerant quantum circuits.

The von Neumann architecture for a classical computer comprises a central processing unit and a memory holding instructions and data. We demonstrate a quantum central processing unit that exchanges data with a quantum random-access memory integrated on a chip, with instructions stored on a classical computer. We test our quantum machine by executing codes that involve seven quantum elements: Two superconducting qubits coupled through a quantum bus, two quantum memories, and two zeroing registers. Two vital algorithms for quantum computing are demonstrated, the quantum Fourier transform, with 66% process fidelity, and the three-qubit Toffoli-class OR phase gate, with 98% phase fidelity. Our results, in combination especially with longer qubit coherence, illustrate a potentially viable approach to factoring numbers and implementing simple quantum error correction codes.

AbstractA generator of rectangular voltage pulses with an amplitude of ~30 kV, a rise time of ~1.5 µs, and a duration of up to 10 µs is described that contains a step-up pulse transformer, as well as thyristor switches with low and high operating voltages, which form, respectively, the front and fall of output pulses. The possibility of generating volume discharges with a frequency of 1 kHz in a barrier-type reactor designed for biological research is shown.

AbstractMonounit and modular switches of high-power current pulses with an operating voltage of 12 kV, made on the basis of series-connected shock ionized dynistors, are described. The switching processes of these switches are studied. The dependence of switching energy losses on the control pulse power is determined. The possibility of switching nanosecond current pulses with an amplitude of several kiloamperes at a frequency of several hundred hertz is shown.

I developed a mathematical method to search for DNA regions that are significantly enriched in reverse complement triplets (RCTs) and are located in sequences with strongly expressed triplet periodicity (TP). The method makes it possible to exclude the influence of TP on the number of RCTs. To search for RCTs, I used the difference between triplet frequencies and their expected number, which was determined by taking into account the TP of the analyzed region. I analyzed the genomes of 42 bacteria representing all bacterial phyla, and found that the number of DNA regions containing RCTs ranged from several hundred to several thousand per genome depending on its size. The average length of the region was about 850 DNA bases. The most common inversion symmetry (IS) pattern of the RCT-containing regions was the enrichment of the first, second, and third triplet positions with A, G, A, T, and T, C bases, respectively. When the sequence was rotated 180 degrees and the bases were replaced with complementary ones (IS), such enrichment of triplet positions was preserved. I suggest that the emergence of IS could be a result of evolutionary processes such as inversions, transpositions, and recombinations.

AbstractA high-power generator based on small TB133-250-24 thyristors, which contains four thyristor modules with an operating voltage of 24 kV, is considered. The parameters of control pulses and protective circuits that provide low switching energy losses in series-connected thyristors and the absence of dangerous overvoltages upon their enabling are determined. The results of generator testing at a frequency of 10 Hz are presented. It is able to switch microsecond current pulses with an amplitude of 12 kA and a front of 0.8 μs. The possibility of scaling these results is shown.

AbstractThe results of experimental studies of optimized shock-ionized dynistors (SIDs) when switching high-power current pulses with a nanosecond duration are presented. It is shown that the efficiency of the SID switching process can be increased by introducing uniformly distributed equal-sized diode sections, whose total area is significantly less than the total area of the semiconductor structure of the dynistor, into its four-layer structure. The results of comparative studies of optimized SIDs with different areas of structures and different maximum allowable voltages in the stationary state are presented. Explanations of the results are given.

AbstractThe results of optimizing a high-power switch that consists of a block of reversely switched-on dynistors with 50-mm diameter structures, a dynistor triggering unit, and a choke with a saturable core, which reduces the power of the triggering unit by creating a delay of a sharp increase in the main current during the flow of the control current having the opposite polarity, are presented. It is shown that the reduction of the traditional microsecond duration of the triggering action to several hundred nanoseconds, which is required for a significant reduction in the choke dimensions and inductance, does not lead to an increase in energy losses in dynistors if the control current has a sufficiently large amplitude and the magnitude of the triggering charge does not change. The design of an optimized switch having an inductance of ~200 nH and an operating voltage of 16 kV is described. The possibility of its long-term use for switching current pulses with an amplitude of ~100 kA that increase at a rate of ~30 kA/μs is shown.