Radio frequency measurements of tunnel couplings and singlet–triplet spin states in Si:P quantum dots

Spin states of the electrons and nuclei of phosphorus donors in silicon are strong candidates for quantum information processing applications given their excellent coherence times. Designing a scalable donor-based quantum computer will require both knowledge of the relationship between device geometry and electron tunnel couplings, and a spin readout strategy that uses minimal physical space in the device. Here we use radio frequency reflectometry to measure singlet–triplet states of a few-donor Si:P double quantum dot and demonstrate that the exchange energy can be tuned by at least two orders of magnitude, from 20 μeV to 8 meV. We measure dot–lead tunnel rates by analysis of the reflected signal and show that they change from 100 MHz to 22 GHz as the number of electrons on a quantum dot is increased from 1 to 4. These techniques present an approach for characterizing, operating and engineering scalable qubit devices based on donors in silicon

Ring-Opening Copolymerization of L-Lactide and Epsilon-Caprolactone in Supercritical Carbon Dioxide Using Triblock Oligomers of Caprolactone and Peg As Stabilizers

In this study, the use of triblock (A-B-A) oligomers of epsilon-caprolactone (epsilon-CL) (A) and PEG400 (B) as stabilizers (SB) for the copolymerization of L-lactide (LLA) and epsilon-CL in supercritical carbon dioxide (scCO(2)) was investigated. To determine the effect of CO2-philic and polymer-philic segments on copolymerization, oligomers with three different average molecular weights (M-w=2000-6000 Da) were synthesized by changing the PEG400/epsilon-CL ratio. Copolymerizations were confirmed by H-1-nuclear magnetic resonance (NMR), C-13-NMR and differential scanning calorimeter data. It was possible to copolymerize LLA and e-CL in scCO(2) without any SB; however, the polymerization yields and average molecular weights were low, and significant aggregate formations were detected. Recipes featuring only 5% SB were successfully applied to reach high polymerization yields of similar to 85% and polymers with average molecular weights greater than 20 kDa. When the polymer-philic segment of the SB increased, both the yield and molecular weight of the copolymer also increased significantly, resulting in white powdery products. Polymer Journal (2011) 43, 785-791; doi: 10.1038/pj.2011.70; published online 27 July 2011Wo

Creatine supplementation with specific view to exercise/sports performance: An update

Creatine is one of the most popular and widely researched natural supplements. The majority of studies have focused on the effects of creatine monohydrate on performance and health; however, many other forms of creatine exist and are commercially available in the sports nutrition/supplement market. Regardless of the form, supplementation with creatine has regularly shown to increase strength, fat free mass, and muscle morphology with concurrent heavy resistance training more than resistance training alone. Creatine may be of benefit in other modes of exercise such as high-intensity sprints or endurance training. However, it appears that the effects of creatine diminish as the length of time spent exercising increases. Even though not all individuals respond similarly to creatine supplementation, it is generally accepted that its supplementation increases creatine storage and promotes a faster regeneration of adenosine triphosphate between high intensity exercises. These improved outcomes will increase performance and promote greater training adaptations. More recent research suggests that creatine supplementation in amounts of 0.1 g/kg of body weight combined with resistance training improves training adaptations at a cellular and sub-cellular level. Finally, although presently ingesting creatine as an oral supplement is considered safe and ethical, the perception of safety cannot be guaranteed, especially when administered for long period of time to different populations (athletes, sedentary, patient, active, young or elderly)