Unstable Atoms Research Articles

Nitrogen Complex-Driven Vacancy Cluster in Group-III Nitrides.

A series of experiments have elucidated the primary defects in group-III nitride epilayers, identifying vacancy clusters due to cation migration at interfaces to mitigate strained lattice. While the occurrence of these defects is well-documented, the underlying electronic mechanisms driving vacancy agglomeration in nitrides and their alloys remain poorly understood. In this study, we uncovered a previously unreported ground state of two metal vacancies driven by the migration of kinetically unstable nitrogen atoms using an ab initio approach. Our findings reveal that the mixed covalent-ionic bond character of nitrides is a crucial factor in determining the stability of vacancy clusters. Notably, the relatively strong ionic character of AlN facilitates the formation of exceptionally stable vacancy clusters with a pyramidal nitrogen complex. In contrast, GaN, despite having similar covalent bonding strength, exhibits less stable vacancy clusters due to its weaker ionic character. Moreover, in InN, we observe the formation of molecular-like azide anion that creates a trimer metallic-like bond between indium dangling bonds, accompanied by vigorous indium migration. In the process, we newly identified the formation of a Schottky-Frenkel composite defect. We believe that these novel insights into the bond character and stability of vacancy clusters in nitrides provide a new understanding that could drive the design and optimization of nitride-based materials and electronic devices.

Free radicals, antioxidants and functional foods: impact on human health

Free radicals are unstable atoms that can harm cells and have a role in ageing and a number of disorders.In addition to being created by the body naturally, they can also be absorbed from outside sources like cigarette smoke and pollution. Many chronic health issues, including cancer, cataracts, inflammatory and cardiovascular diseases, are partly caused by the damage caused by free radicals. Antioxidants stop radicals from forming, which stops tissue damage caused by free radicals. Our body produces reactive oxygen species (ROS), reactive nitrogen species, and free radicals when it is exposed to varied physiochemical situations, pathological states, or other endogenous systems. Correct physiological function requires a balance between antioxidants and free radicals. Oxidative stress is the result of free radicals surpassing the body's capacity to control them. Because functional foods suppress acetylcholinesterase, they may be able to treat dementia and Alzheimer's disease. Similarly, treatments based on the presence of antioxidants, herbs, and spices may also be beneficial.

For the regeneration of spent graphite: The exploring of structural failure mechanism about commercial graphite

Along with the wide application of electric automobiles, the great “wave” of recycling for lithium-ion batteries would be upcoming due to their limited cycling lifespan. As the main components but without valuable elements, spent graphite suffers from effective recycling manners. Although the regeneration method has been deemed as a promising manner, the clarifying of their failure mechanism is prerequisite to the exploring of regeneration methods. Herein, commercial graphite with different healthy states is prepared through the disassembling of cells at different cycles. Assisted by the detailed structural analysis, the systematic failure process is clearly illustrated. At initial cycling, the shuttling of lithium ions renders the decomposing of unstable carbon atoms and some weak interlayer structures. With further cycling, the interlayer architecture and large-size grains were further damaged, to form small-size grains, accompanying enhanced anisotropy, finally resulting in the increasing internal resistance. Moreover, owing to the ion-diffusion behaviors, graphite sheets have an obvious moving, resulting in the transformation from 2H-phase to 3R-phase with the decreasing of energy-storage activity. Thus, from the perspective of internal structure, the decreasing of graphitized grains and the formation of 3R-phase served as crucial failure factors. Given this, the work is anticipated to illustrate the failure mechanism of graphite, meanwhile offering the basic regeneration direction of spent graphite samples.

Enhancing mechanical properties of polyvinyl chloride: Novel organic‐modified cinnamate‐intercalated calcium aluminum hydrotalcite as a high‐efficiency thermal stabilizer

AbstractTo make the hydrotalcite uniformly dispersed in polyvinyl chloride (PVC) and enhance its thermal stability, cinnamate‐intercalated calcium aluminum hydrotalcite (CaAl‐cinnamate‐LDHs) underwent organic modification with cetyltrimethylammonium bromide/sodium dodecyl sulfate/polyethylene glycol (CTAB/SDS/PEG). The structures of modified hydrotalcite were characterized using x‐ray diffractometer, scanning electron microscope, particle size analysis, and water contact angle test. The thermal stability was assessed through thermal aging oven experiment, Congo Red experiment, and thermogravimetric experiment, revealing their exceptional performance. Simultaneously, the synergistic effect of PEG‐LDHs with auxiliary thermal stabilizers was examined, with epoxy soybean oil proving to be the most effective, which made the PVC sample incompletely black within 120 min. Mechanical properties and dynamic thermomechanical analysis indicated that the overall mechanical characteristics of the PVC samples with modified hydrotalcite were significantly superior to the unmodified CaAl‐cinnamate‐LDHs. Additionally, the optical performance test demonstrated excellent transparency in the PEG‐LDHs/PVC sample. Through analyzing the thermal stability mechanism, it was indicated that hydrotalcite effectively absorbed HCl. Furthermore, the combination of PEG‐LDHs and ESO replaced unstable Cl atoms and reacted with conjugated double bonds, thereby reducing the aging and discoloration of PVC.Highlights The modified hydrotalcite preparation process was simple and easy to operate. The CTAB/SDS/PEG‐LDHs/PVC samples exhibited excellent thermal stability. Mechanical properties of the PVC samples with modified hydrotalcite were significantly superior to the unmodified CaAl‐cinnamate‐LDHs.

Health Effects of Ionizing Radiation on the Human Body.

Radioactivity is a process in which the nuclei of unstable atoms spontaneously decay, producing other nuclei and releasing energy in the form of ionizing radiation in the form of alpha (α) and beta (β) particles as well as the emission of gamma (γ) electromagnetic waves. People may be exposed to radiation in various forms, as casualties of nuclear accidents, workers in power plants, or while working and using different radiation sources in medicine and health care. Acute radiation syndrome (ARS) occurs in subjects exposed to a very high dose of radiation in a very short period of time. Each form of radiation has a unique pathophysiological effect. Unfortunately, higher organisms-human beings-in the course of evolution have not acquired receptors for the direct "capture" of radiation energy, which is transferred at the level of DNA, cells, tissues, and organs. Radiation in biological systems depends on the amount of absorbed energy and its spatial distribution, particularly depending on the linear energy transfer (LET). Photon radiation with low LET leads to homogeneous energy deposition in the entire tissue volume. On the other hand, radiation with a high LET produces a fast Bragg peak, which generates a low input dose, whereby the penetration depth into the tissue increases with the radiation energy. The consequences are mutations, apoptosis, the development of cancer, and cell death. The most sensitive cells are those that divide intensively-bone marrow cells, digestive tract cells, reproductive cells, and skin cells. The health care system and the public should raise awareness of the consequences of ionizing radiation. Therefore, our aim is to identify the consequences of ARS taking into account radiation damage to the respiratory system, nervous system, hematopoietic system, gastrointestinal tract, and skin.

A “one‐pot” method for synthesizing zinc tryptophan and its derivatives as highly efficient PVC thermal stabilizer with excellent mechanical properties

AbstractZinc Tryptophan (Trp‐Zn) and zinc N‐(salicylic) tryptophan (SalTrp‐Zn) were synthesized from tryptophan, zinc acetate, and salicylic aldehyde by one‐pot method, respectively. The structure was analyzed by FT‐IR, 1H NMR, and elemental analysis. PVC samples were prepared by stirring method and solvent film process, and then the thermal properties of PVC samples were studied by thermal aging chamber test, Congo red test, electrical conductivity test, and thermogravimetric analysis (TGA). The thermal stability of Trp‐Zn and SalTrp‐Zn stabilized PVC samples was better than calcium and zinc soaps used in industry. The thermal stability time was up to 80 min, and it was a long‐acting thermal stabilizer. After the addition of CaSt2 and Trp‐Zn stabilizer in different proportions, the thermal stability of PVC was obviously improved, and the initial whiteness of the film was improved after the combination of Trp‐Zn/SalTrp‐Zn. In addition, the tensile test verified that the PVC samples stabilized by Trp‐Zn and SalTrp‐Zn had the highest elongation at break. The addition of Trp‐Zn can reduce the elastic modulus of PVC, effectively improve the mechanical properties of PVC, and make the PVC film have better toughness and elasticity. Through DMA and EDS tests, it can be seen that Trp, SalTrp‐Zn had good compatibility with PVC and DOP. The quantum chemical calculation of Trp‐Zn, SalTrp‐Zn and vinyl chloride models was carried out, and the thermal stability mechanism of thermal stabilizer on PVC was analyzed accurately, mainly the absorption mechanism of HCl and the substitution mechanism of unstable chlorine atoms.

Studies Studies on the phytochemicals of clove and their biological activities

Cloves are a fragrant spice made from the dried flowers of the clove tree. In the past, spices used to be worth their weight in gold, and cloves were no exception. Today, cloves remain a popular spice that gives many dishes subtly sweet warmth. A drop of clove oil is 400 times more powerful as an anti-oxidant than wolf berries or blueberries. Cloves contain a lot of manganese, a mineral that helps your body manage the enzymes that help repair your bones and make hormones. Manganese can also act as an antioxidant that protects your body from harmful free radicals (unstable atoms that cause cell damage). Cloves are a fragrant, dense spice that can be added to both savory dishes (such as curries) and sweet desserts (such as pumpkin pie). They're full of powerful nutrients that help protect your cells from damage. Some natural compounds in cloves interfere with medicines or cause side effects that can be life-threatening. So, it's safest to only cook or bake with cloves and enjoy this spice's health benefits that way. Clove is utilized in cosmetics, medicine, gastronomy, and agriculture due to its abundance of bioactive components such as gallic acid, flavonoids, eugenol acetate, and eugenol. Clove essential oil has been revealed to have antibacterial, antinociceptive, antibacterial activities, antifungal, and anticancerous qualities. Anti-inflammatory chemicals, including eugenol and flavonoids, are found in clove that help decrease inflammation and alleviate pain. The anti-inflammatory and analgesic qualities of clove oil have made it a popular natural cure for toothaches and gum discomfort. Due to its therapeutic potential, it has been used as a bioactive ingredient in coating fresh fruits and vegetables. This research article outlines the potential food processing applications of clove essential oil. The chemical structures of components, bioactive properties, and medicinal potential of clove essential oil, including phytochemical importance in food, have also been thoroughly addressed.

The tandem catalysis of porous CoW composite oxide: Intensified allylic oxidation of cyclohexene to 2-cyclohexene-1-one

The controllable oxidation of the allylic CH bond has great academic and industrial value. Different Co/W ratios of CoW composite oxides were prepared using hydrothermal method and used in the allylic oxidation reaction of cyclohexene containing unstable allylic hydrogen atoms and carbon-carbon double bonds. The relationship between the structure of active sites and catalytic performance was revealed using characterization techniques such as XRD, N2 adsorption/desorption, SEM, TEM, FT-IR, UV–vis, and XPS. The results indicated that the Co(II)/Co(III) sites effectively mediate the first step of the entire oxidation reaction system, which generates hydroxyl radicals and peroxyl radicals through the activation of H2O2 to achieve chain initiation. Subsequently, the cyclohexene underwent a series of chain migration reactions under the action of hydroxyl radicals and peroxyl radicals, resulting in the formation of 2-cyclohexen-1-one and 2-cyclohexen-1-ol. Finally, 2-cyclohexen-1-ol interacted with W(VI) sites to form 2-cyclohexen-1-one via an alcohol-coordinated hydroxyl intermediate. The tandem oxidation reaction of cyclohexene allylic oxidation and 2-cyclohexen-1-ol dehydrogenation was realized by the CoW synergistic catalytic. The synergy between Co and W sites, composed of Co-O-W units on the surface of the CoW oxide with porous channel features, was elucidated. The experimental results showed that under the optimal conditions, using CoW composite oxide (Co/W = 1:1) as the catalyst, a 79.8% conversion rate of cyclohexene was achieved with 93.9% selectivity for the allylic products, among which the selectivity for 2-cyclohexen-1-one was 73.8%.

ANALYSIS OF THE PRODUCTION OF RARE-EARTH ISOTOPES AT THE WWR-K RESEARCH REACTOR: PROMISING THERAPEUTIC RADIONUCLIDES

Rare Earth Elements (REE) are a group of seventeen chemical elements in the periodic table, including lanthanides and scandium and yttrium. These elements have unique physical and chemical properties that make them valuable in various industries, including electronics, magnets, and catalysts. However, radioactive isotopes of rare earth elements also possess effective nuclear physical properties that make them promising for the development of new radiopharmaceuticals for therapeutic purposes. These radioactive isotopes have unstable atoms with excess nuclear energy, and they undergo radioactive decay, which can be utilized for medical applications.The nuclear physical properties of radioactive isotopes of rare earth elements make them suitable for therapeutic purposes in medicine. For example, technetium-99m, a radioactive isotope of technetium, is widely used in diagnostic nuclear medicine due to its outstanding physical-chemical characteristics. Other radioactive isotopes of rare earth elements, such as holmium-166, have been established for a broad spectrum of medical applications. These isotopes can be used in targeted radiation therapy to treat various diseases, including cancer. The unique properties of these radioactive isotopes allow for precise targeting and delivery of radiation to specific tissues or cells, minimizing damage to healthy tissues.The potential of radioactive isotopes of rare earth elements for therapeutic purposes extends beyond the current applications. Ongoing research and innovations in the field of radiopharmaceuticals continue to explore the use of underutilized lanthanoid radionuclides for theranostic purposes. For example, astatine, a rare and highly radioactive element, exhibits multiple isotopes that can be potentially utilized in targeted therapy. The development of new radiopharmaceuticals using radioactive isotopes of rare earth elements holds promise for advancing medical treatments and improving patient outcomes. With further research and advancements, these isotopes may play a crucial role in the future of therapeutic medicine.This research work makes it possible to evaluate the possibility of obtaining REE such radioisotopes as: 90Y, 141Ce, 147Nd, 153Sm, 165Dy, 166Ho, 169Tm, 175Yb, 177Yb, 177Lu by reaction (n, γ) at the WWR-K reactor.

Ce dissolution induced in situ generating oxygen defects of Co3O4 boosting electrocatalytic oxidation of 5-hydroxymethylfurfural

The dissolution of unstable metal atoms can form structures with more defects on the catalyst surface, which provides great feasibility for improving the intrinsic activity of catalyst. In this paper, it is proposed that the dissolution of doped Ce promotes the in-situ formation of oxygen vacancy in the electrocatalytic oxidation of 5-hydroxymethylfurfural (HMFOR) process, which is conducive to the rate-determining step of dehydrogenation of the reaction intermediates, and thus accelerates the HMFOR. The Ce-Co3O4 exhibits excellent HMFOR performance with impressive HMF conversion (98.0%), 2,5-furandicarboxylic acid (FDCA) yield (95.48%), and Faradaic efficiency (97%) at 1.45 V vs. RHE. In situ Raman proved that the dissolution of doped Ce was accompanied by the formation of oxygen vacancy on the surface of Co3O4, and the in situ generated oxygen vacancy not only regulated the adsorption balance of *OH and HMF in the HMFOR process, but also promoted the formation of high valence cobalt. This in situ vacancy generation strategy provides a new reference for future directions in designing highly efficient electrocatalyst for biomass conversion.

Essential Oils – Anti-Microbial and Pharmacological Properties of Essential Oils

The oils that are essential are highly concentrated herbal extracts from extremely significant botanicals. Popularly these oils are used in complementary and substitute medicine. The oil is usually extracted from flowers, leaves, roots, and added parts of plants. The antimicrobial activity of essential oils and their components has been studied for a very long time. Essential oils are produced from a complex combination of unstable atoms that are delivered by the optional digestion of sweet-smelling and medicinal plants and can be produced by various techniques, including distillation or microwaves. The huge number of studies on the antimicrobial action of essential oils has permitted the logical acknowledgment of these mixtures on the control of a wide scope of microbial microorganisms. The advances made on the examination of the method of activity of essential oils against bacterial cell targets give us new points of view to battle constant and antimicrobial safe bacterial microorganisms.

A large-momentum-transfer matter-wave interferometer to measure the effect of gravity on positronium

This paper reports the study of a new interferometric configuration to measure the effect of gravity on positronium. A Mach–Zehnder matter-wave interferometer has been designed to operate with single-photon transitions and to transfer high momentum to a 200 eV positronium beam. The work shows the results and methods used to simulate the interferometer and estimate the operating parameters and the time needed to perform the experiment. It has been estimated that within less than 1 year, the acquisition time is sufficient to achieve a 10% accuracy level in measuring positronium gravitational acceleration, even with a poorly collimated beam, which is significant for theoretical models describing matter–antimatter symmetry. These results pave the way for single photon transition large momentum transfer interferometry with fast atomic beams, which is particularly useful for studies with antimatter and unstable atoms.

Probing the Free Volume in Polymers by Means of Positron Annihilation Lifetime Spectroscopy.

Positron annihilation lifetime spectroscopy (PALS) is a valuable technique to investigate defects in solids, such as vacancy clusters and grain boundaries in metals and alloys, as well as lattice imperfections in semiconductors. Positron spectroscopy is able to reveal the size, structure and concentration of vacancies with a sensitivity of 10-7. In the field of porous and amorphous systems, PALS can probe cavities in the range from a few tenths up to several tens of nm. In the case of polymers, PALS is one of the few techniques able to give information on the holes forming the free volume. This quantity, which cannot be measured with macroscopic techniques, is correlated to important mechanical, thermal, and transport properties of polymers. It can be deduced theoretically by applying suitable equations of state derived by cell models, and PALS supplies a quantitative measure of the free volume by probing the corresponding sub-nanometric holes. The system used is positronium (Ps), an unstable atom formed by a positron and an electron, whose lifetime can be related to the typical size of the holes. When analyzed in terms of continuous lifetimes, the positron annihilation spectrum allows one to gain insight into the distribution of the free volume holes, an almost unique feature of this technique. The present paper is an overview of PALS, addressed in particular to readers not familiar with this technique, with emphasis on the experimental aspects. After a general introduction on free volume, positronium, and the experimental apparatus needed to acquire the corresponding lifetime, some of the recent results obtained by various groups will be shown, highlighting the connections between the free volume as probed by PALS and structural properties of the investigated materials.

A new organic zinc thermal stabilizer containing two kinds of anions with excellent thermal stability on polyvinyl chloride by multistep substitution

AbstractA new kind of highly efficient organic zinc thermal stabilizer for polyvinyl chloride (PVC), zinc arginine stearate [Zn(Arg)(St)], is designed by introducing the arginine and stearate to the same zinc atoms to regulate the binding energy between anions and cation. Gaussian soft is used to calculate the binding energy. The results of Fourier transform infrared spectra, elemental analysis, thermogravimetric analysis, and differential scanning calorimetry show that Zn(Arg)(St) has been successfully synthesized. Zn(Arg)(St) stabilized PVC displays excellent Congo red, static and dynamic thermal stability time, especially the excellent initial whiteness and whiteness retention time. The thermal stability mechanism of Zn(Arg)(St) attributes to the different binding energy between the two anions and zinc cation, which results in Zn(Arg)(St) continuously replacing the unstable chlorine atoms step by step by Arg and St anions. Moreover, the amino group in Arg could complex ZnCl2 to inhibit the “zinc burning” effect, and the guanidine group could absorb HCl to inhibit the “autocatalytic effect” of HCl. In addition, Zn(Arg)(St) has a remarkable lubrication effect, which also enhances the thermal stability of PVC. Thus, Zn(Arg)(St) is an environmentally friendly thermal stabilizer for PVC with an excellent thermal stability effect. Importantly, this work also proposes a new method to design highly efficient thermal stabilizers for PVC.

Synthesis of zinc Schiff base complex and its application as highly efficient thermal stabilizer for flexible poly (vinyl chloride)

N, N'-bis (salicylaldehyde) ethyldiamino-zinc (BSE-Zn) was synthesized from salicylaldehyde and ethylenediamine. Its structure was analyzed by FT-IR, 1H NMR and elemental analysis. The thermal properties of PVC samples were studied by thermal aging oven test, Congo red test, conductivity test, thermogravimetric analysis (TGA) and UV–Visible spectroscopy (UV–Vis). The thermal stability of BSE-Zn stabilized PVC samples was better than the calcium zinc soaps used in industry. The thermal stability time can be as long as 90 min, which proved that BSE-Zn was a long-term thermal stabilizer. By blending CaSt2 and BSE-Zn stabilizer in different proportions, the thermal stability of PVC was significantly improved while improving the initial color. When the compound ratio is CaSt2/BSE-Zn=2:1, the thermal stability of PVC sample was best and didn't age until 120 min. In addition, it was verified by tensile test that the PVC sample stabilized by BSE-Zn had the highest tensile strength and elongation at break, which could improve the mechanical properties of PVC and make the PVC film have better toughness and elasticity. the quantum chemical calculation of BSE-Zn and vinyl chloride models was carried out, and the thermal stability mechanism of BSE-Zn on PVC was analyzed accurately, mainly the absorption mechanism of HCl and the replacement mechanism of unstable chlorine atoms.

The Promoting Effect of Multifunctional Groups on the Thermal and Mechanical Properties of PVC Materials

The development of PVC materials grafted with mannich base originated from myrcene (P-MAM-g, where the mannich base derived from myrcene is abbreviated as MAM) via green and effective synthetic methods is a good strategy to avoid unacceptable discoloration and deterioration of thermal and mechanical properties caused by autocatalytic dehydrochlorination (DHC) during PVC processing. In this study, MAM with double bonds, amino groups, ester groups, and phospholipid groups was introduced into the chains of PVC to improve the thermal stability of PVC. The experimental results showed that the covalent attachment of MAM to PVC enhanced both the initial and the long-term stability of PVC. The enhanced performance of P-MAM-g compared with unmodified PVC is attributed to the simultaneous introduction of double bonds and amino groups into the PVC structure. The double bonds trapped the unstable chlorine atoms originated from the degradation of the PVC chain and reacted with the labile macromolecular radicals originated from PVC, thus inhibiting the radical degradation of the PVC chain. Furthermore, the amino groups absorbed the HCl produced in the degradation of PVC, inhibiting the adverse effects of HCl. P-MAM-g displayed better intrinsic flexibility and anti-migration ability of organic functional components compared with the control PVC materials. A possible stabilizing mechanism of the P-MAM-g was also presented.

Rare earth Ce based metal organic framework as efficient synergistic thermal stabilizer for PVC: Preparation and thermal stabilization behavior

The complex production process and uneven performance seriously restrict the application of Rare earth thermal stabilizer. In this study, the thermal stability behavior of metal organic framework Ce(1,3,5-BTC)(H2O)6 (Ce-BTC) towards PVC was studied. Experimental results showed that the combination of Ce-BTC, 2,4,6-tris[di(hydroxymethyl) amino]-1,3,5-triazine (HHTT), and ESBO synergistically stabilized PVC sample displayed significantly improved initial color, meanwhile, the Ts and the time of "zinc burning" were prolonged to 55.17 and 70 min, respectively, as well. During thermal treatment, HHTT can replace the unstable chlorine atoms on the PVC chain, and the incompletely coordinated Ce ions in Ce-BTC can inhibit the further polymerization of conjugated polyenes by reacting with the alkene chain resulted from PVC degradation, these two factors synertistically inhibit the degradation of PVC. The nertralization of HCl by HHTT and ESBO can provide longer reaction time for incompletely coordinated Ce ions and chlorine atoms, delaying the autocatalytic effect of HCl.

Structure-based design, synthesis and evaluation of a novel family of PEX5-PEX14 interaction inhibitors against Trypanosoma

Trypanosomiases are neglected tropical diseases caused by Trypanosoma (sub)species. Available treatments are limited and have considerable adverse effects and questionable efficacy in the chronic stage of the disease, urgently calling for the identification of new targets and drug candidates.Recently, we have shown that impairment of glycosomal protein import by the inhibition of the PEX5-PEX14 protein-protein interaction (PPI) is lethal to Trypanosoma. Here, we report the development of a novel dibenzo[b,f][1,4]oxazepin-11(10H)-one scaffold for small molecule inhibitors of PEX5-PEX14 PPI. The initial hit was identified by a high throughput screening (HTS) of a library of compounds. A bioisosteric replacement approach allowed to replace the metabolically unstable sulphur atom from the initial dibenzo[b,f][1,4]thiazepin-11(10H)-one HTS hit with oxygen. A crystal structure of the hit compound bound to PEX14 surface facilitated the rational design of the compound series accessible by a straightforward chemistry for the initial structure-activity relationship (SAR) analysis. This guided the design of compounds with trypanocidal activity in cell-based assays providing a promising starting point for the development of new drug candidates to tackle trypanosomiases.

Dynamics of Open Quantum Systems—Markovian Semigroups and Beyond

The idea of an open quantum system was introduced in the 1950s as a response to the problems encountered in areas such as nuclear magnetic resonance and the decay of unstable atoms. Nowadays, dynamical models of open quantum systems have become essential components in many applications of quantum mechanics. This paper provides an overview of the fundamental concepts of open quantum systems. All underlying definitions, algebraic methods and crucial theorems are presented. In particular, dynamical semigroups with corresponding time-independent generators are characterized. Furthermore, evolution models that induce memory effects are discussed. Finally, measures of non-Markovianity are recapped and interpreted from a perspective of physical relevance.

Experimental evidence for fractional valence of La in LaAl2 : Electronic structure from x-ray photoelectron spectroscopy and band structure calculations

We confirmed the fractional filling of the $4f$ shell of La in ${\mathrm{LaAl}}_{2}$ by x-ray photoemission spectroscopy (XPS) and ab initio calculations. The La $3d$ core-level XPS spectra were analyzed by use of the Gunnarsson-Sch\"onhammer theoretical model, which allowed us to determine the valency of La smaller than 3 ($v=2.9$). A similar occupation of the La $4f$ shell results from the band structure calculations. In real unstable La atom charge is transferred in the mixing process from its outer $5d6s$ electron shells to the local $4f$ state, according to $4{f}^{\ensuremath{\nu}}(5{d}^{1\ensuremath{-}\ensuremath{\nu}}6{s}^{2})$, where $0<\ensuremath{\nu}\ensuremath{\ll}1$. The calculated density of states fit well the valence band XPS spectra. We have shown that the fractional valence of La plays a key role in electric transport properties of ${\mathrm{LaAl}}_{2}$ and the fractional filling of the $4f$ shell is really at the root of the resistivity anomalies either at the high or low temperatures.