Modern Physics Letters B

Briefly, we reviewed the latest progress in energy conversion efficiency and degradation rate of the quantum dot (QD) solar cells. QDs are zero dimension nanoparticles with tunable size and accordingly tunable band gap. The maximum performance of the most advanced QD solar cells was reported to be around 10%. Nevertheless, majority of research groups do not investigate the stability of such devices. QDs are cheaper replacements for silicon or other thin film materials with a great potential to significantly increase the photon conversion efficiency via two ways: (i) creating multiple excitons by absorbing a single hot photon, and (ii) formation of intermediate bands (IBs) in the band gap of the background semiconductor that enables the absorption of low energy photons (two-step absorption of sub-band gap photons). Apart from low conversion efficiency, QD solar cells also suffer from instability under real operation and stress conditions. Strain, dislocations and variation in size of the dots (under pressure of the other layers) are the main degradation resources. While some new materials (i.e. perovskites) showed an acceptable high performance, the QD devices are still inefficient with an almost medium rate of 4% (2010) to 10% (2015).

A number of measurements have been provided to detect formaldehyde in the atmosphere, but there are no clear unified standards in engine exhaust. Nowadays, formaldehyde, an unregulated emission from methanol engine, has been attracting increasing attention by researchers. This paper presents the detection techniques for formaldehyde emitted from the engines applied in recent market, introducing the approaches in terms of unregulated emission tests of formaldehyde, which involved gas chromatography, liquid chromatography, chromatography-mass spectrometry, chromatography-spectrum, Fourier infrared spectroscopy and spectrophotometry. The author also introduces the comparison regarding to the advantages of the existing detection techniques based on the principle, to compare with engine exhaust sampling method, the treatment in advance of detection, obtaining approaches accessing to the qualitative and quantitative analysis of chromatograms or spectra. The accuratest result obtained was chromatography though it cannot be used continuously. It also can be utilized to develop high requirements of emissions and other regulations. Fourier infrared spectroscopy has the advantage of continuous detection for a variety of unregulated emissions and can be applied to the bench in variable condition. However, its accuracy is not as good as chromatography. As the conclusion, a detection technique is chosen based on different requirements.

Circulating tumor cells (CTCs) are malignant cells that are derived from a solid tumor in the metastasis stage and are shed into the blood stream. These cells hold great promise to be used as liquid biopsy that is less aggressive than traditional biopsy. Recently, detection and enumeration of these cells has received ever-increasing attention from researchers as a way of early detection of cancer metastasis, determining the effectiveness of treatment and studying the mechanism of formation of secondary tumors. CTCs are found in blood at low concentration, which is a major limitation of isolation and detection of these cells. Over the last few years, multifarious research studies have been conducted on accurate isolation and detection and post processing of CTCs. Among all the proposed systems, microfluidic systems seem to be more attractive for researchers due to their numerous advantages. On the other hand, recent developments in optical methods have made the possibility of cellular studies at single-cell level. Thus, accuracy and efficiency of separation, detection and manipulation of CTCs can be improved using optical techniques. In this review, we describe optical methods that have been used for CTC detection, manipulation and post processing.

The room-temperature structural phase transition of graphite at elevated hydrostatic pressure has drawn considerable scientific interest for its fundamental importance in condensed matter physics and materials science over the past few decades. A pressure-induced phase transition has been demonstrated in previous experiments by the measurement of electrical resistance, optical spectrum, X-ray diffraction spectrum, inelastic X-ray scattering and Raman spectroscopy. However, the nature of the cold-compressed graphite phase has been puzzling the experts and pioneers in the field of high pressure research due to some inherent factors, until recently a monoclinic structure, i.e. $M$-carbon, stands out from the other structure candidates and successfully accounts for the crystal structure of the cold-compressed graphite phase both in theory and experiment that eventually putting an end to this long-lasting controversial issue. This paper reviews the recent progress on the pressure-induced phase transitions of graphite at room temperature especially for the theoretical investigations. The review will focus on the recent proposed novel carbon allotropes as candidate structures of the cold-compressed graphite phase by using different crystal structure prediction methods. The history of structure determination of cold-compressed graphite phase is discussed.

The radical-pair mechanism (RPM) was introduced in the 1960s to explain anomalously large EPR and NMR signals in chemical reactions of organic molecules. It has evolved to the cornerstone of spin chemistry, the study of the effect electron and nuclear spins have on chemical reactions, with the avian magnetic compass mechanism and the photosynthetic reaction center dynamics being prominent biophysical manifestations of such effects. In recent years the RPM was shown to be an ideal biological system where the conceptual tools of quantum-information science can be fruitfully applied. We will here review recent work making the case that RPM is indeed a major driving force of the emerging field of quantum biology.

A microscopic model is proposed to describing the multiferroic properties in $R{\mathrm{\text{CrO}}}_3$, where $R$ is the magnetic rare earth ion. Using the Green’s function theory, the weak ferromagnetism and the coercive field are calculated by a balance between the Dzyaloshinskii–Moriya interaction (DMI), the single-ion anisotropy and the exchange interaction. We have discussed the magnetic rotational spin-reorientation (SR) transition between ${\mathrm{\Gamma }}_4$ and ${\mathrm{\Gamma }}_2$ phases in ${\mathrm{\text{SmCrO}}}_3$ and the abrupt one between ${\mathrm{\Gamma }}_4$ and ${\mathrm{\Gamma }}_1$ in ${\mathrm{\text{ErCrO}}}_3$ calculating the energies in the corresponding phases. The type of the phase transition in $R{\mathrm{\text{CrO}}}_3$ is determined by the sign of the second magnetic anisotropy constant. In order to investigate the origin of the extraordinary ferroelectricity in $R{\mathrm{\text{CrO}}}_3$, we have studied the different contributions in the polarization due to the antisymmetric exchange DMI and the magnetostriction arising from the Cr-ordering. It is shown that the polarization is due to the interaction between the magnetic $R$- and Cr-ions. The influence of a magnetic field on the polarization and of an electric field on the magnetization are also calculated as an evidence for a strong magnetoelectric coupling in $R{\mathrm{\text{CrO}}}_3$.

In this paper, we utilize a family of Hermitian dual-containing constacyclic codes to construct classical and quantum MDS convolutional codes. Our classical and quantum convolutional codes are optimal in the sense that they attain the classical (quantum) generalized Singleton bound.

Modifications with different acids (HNO₃, H₂SO₄, HCl and HF, respectively) were introduced to treat the activated carbons (ACs) surface. The microstructures and surface chemical properties were discussed by X-ray diffraction (XRD), thermogravimetric analysis (TGA), ASAP, Raman spectra and Fourier transform infrared (FTIR) spectra. The ACs electrode-based supercapacitors were assembled with 6 mol ⋅ L${}^{-1}$ KOH electrolyte. The electrochemical properties were studied by galvanostatic charge–discharge and cyclic voltammetry. The results indicated that although the BET surface area of modified ACs decreased, the functional groups were introduced and the ash contents were reduced on the surface of ACs, receiving larger specific capacitance to initial AC. The specific capacitance of ACs modified with HCl, H₂SO₄, HF and HNO₃ increased by 31.4%, 23%, 21% and 11.6%, respectively.