Interaction of theory and experiment: examples from single molecule studies of nanoparticles

This article is in part the author's perspective on the revolution that has occurred in theoretical chemistry during the past half-century. In this period much of theoretical chemistry has moved from its initial emphasis on analytic treatments, resulting in equations for physical chemical and chemical phenomena, to the detailed computation of many different systems and processes. In the best sense the old and the new are complementary and their coexistence can benefit both. Experiment too has seen major developments. One of the newer types of experiment is that of single molecule studies. They range from those on small inorganic and organic nanoparticles to large biological species. We illustrate some of the issues that arise, using the topic of ‘quantum dots’ (QDs), and choosing a particular inorganic nanoparticle, CdSe, the most studied of these systems. Its study reflects the problems that arise in experiment and in theories in this field. The complementary nature of the conventional ensemble experiments and the new single molecule experiments is described and is illustrated by trajectories for the two types of experiments. The research in the QD field is both experimentally and theoretically a currently ongoing process, for which the answers are not fully known in spite of the large body of research. The detailed role of surface states is part of the problem. The field continues to yield new and unexpected results. In a sense this part of the article is an interim report that illustrates one analytic approach to the topic and where computer calculations and simulations can be expected to provide added insight

The Effects of Anabolic-Androgenic Steroids on Gene Expression in Skeletal Muscle: A Systematic Review

International Journal of Exercise Science 16(3): 53-82, 2023. Anabolic-androgenic steroids (AAS) act via androgen receptor (AR) interaction to induce muscle protein synthesis. This process is achieved via altered gene expression via the Notch, Wnt, and Numb pathways and their interactions at the AR, manifesting in key skeletal muscle (SM) phenotypes such as morphology, ion conductance, and functionality. This review aims to report on the effects of AAS administration on gene expression in SM. Peer-reviewed empirical studies evaluating AAS administration on SM phenotypes and gene expression were considered for inclusion. The following databases were searched using a data range of Jan 2000-November 2020: MEDLINE Complete, Academic Search Complete, APA PsycInfo, SPORTDiscus, CINAHL Plus, Cochrane Central Register of Controlled Trials, Rehabilitation & Sports Medicine Source, GreenFILE, and APA PsycArticles. Potential risks of bias were assessed via a modified PEDro Scale. Twenty-nine peer-reviewed titles were included. All studies consisted of either human or rodent subjects and included an AAS dosing protocol, investigated SM phenotypes, and measured gene expression as an outcome variable. Studies investigated the effects of eight AAS compounds across a total of 88 different genes in SM. The most commonly identified genes increased by AAS were IGF, MYOG, and MyoD. There was a general lack of standardized dosing and AAS variety. Future studies should attempt to incorporate multiple AAS compounds and their effects on key SM gene expression

Practical quantum repeaters with linear optics and double-photon guns

We show how to create practical, efficient, quantum repeaters, employing double-photon guns, for long-distance optical quantum communication. The guns create polarization-entangled photon pairs on demand. One such source might be a semiconducter quantum dot, which has the distinct advantage over parametric down-conversion that the probability of creating a photon pair is close to one, while the probability of creating multiple pairs vanishes. The swapping and purifying components are implemented by polarizing beam splitters and probabilistic optical CNOT gates.Comment: 4 pages, 4 figures ReVTe

Evidence for a diffusion-controlled mechanism for fluorescence blinking of colloidal quantum dots

Fluorescence blinking in nanocrystal quantum dots is known to exhibit power-law dynamics, and several different mechanisms have been proposed to explain this behavior. We have extended the measurement of quantum-dot blinking by characterizing fluctuations in the fluorescence of single dots over time scales from microseconds to seconds. The power spectral density of these fluctuations indicates a change in the power-law statistics that occurs at a time scale of several milliseconds, providing an important constraint on possible mechanisms for the blinking. In particular, the observations are consistent with the predictions of models wherein blinking is controlled by diffusion of the energies of electron or hole trap states

A calcium ion in a cavity as a controlled single-photon source

We present a single calcium ion, coupled to a high-finesse cavity, as an almost ideal system for the controlled generation of single photons. Photons from a pump beam are Raman-scattered by the ion into the cavity mode, which subsequently emits the photon into a well-defined output channel. In contrast with comparable atomic systems, the ion is localized at a fixed position in the cavity mode for indefinite times, enabling truly continuous operation of the device. We have performed numeric calculations to assess the performance of the system and present the first experimental indication of single-photon emission in our set-up

Multiple-photon resolving fiber-loop detector

We show first reconstructions of the photon-number distribution obtained with a multi-channel fiber-loop detector. Apart from analyzing the statistics of light pulses this device can serve as a sophisticated postselection device for experiments in quantum optics and quantum information. We quantify its efficiency by means of the Fisher information and compare it to the efficiency of the ideal photodetector.Comment: 5 pages, 6 figure

Is Camouflaging Autistic Traits Associated with Suicidal Thoughts and Behaviours? Expanding the Interpersonal Psychological Theory of Suicide in an Undergraduate Student Sample

The current study explored whether people who camouflage autistic traits are more likely to experience thwarted belongingness and suicidality, as predicted by the Interpersonal Psychological Theory of Suicide (IPTS). 160 undergraduate students (86.9% female, 18–23 years) completed a cross-sectional online survey from 8th February to 30th May 2019 including self-report measures of thwarted belongingness and perceived burdensomeness, autistic traits, depression, anxiety, camouflaging autistic traits, and lifetime suicidality. Results suggest that camouflaging autistic traits is associated with increased risk of experiencing thwarted belongingness and lifetime suicidality. It is important for suicide theories such as the IPTS to include variables relevant to the broader autism phenotype, to increase applicability of models to both autistic and non-autistic people