The point at absolute zero where matter becomes unstable to new forms of order is called a quantum critical point (QCP). The quantum fluctuations between order and disorder 1-5 that develop at this point induce profound transformations in the finite temperature electronic properties of the material. Magnetic fields are ideal for tuning a material as close as possible to a QCP, where the most intense effects of criticality can be studied. A previous study 6 on theheavy-electron material Y bRh 2 Si 2 found that near a field-induced quantum critical point electrons move ever more slowly and scatter off one-another with ever increasing probability, as indicated by a divergence to infinity of the electron effective mass and cross-section. These studies could not shed light on whether these properties were an artifact of the applied field 7,8 , or a more general feature of field-free QCPs. Here we report that when Germanium-doped Y bRh 2 Si 2 is tuned away from a chemically induced quantum critical point by magnetic fields there is a universal behavior in the temperature dependence of the specific heat and resistivity: the characteristic kinetic energy of electrons is directly proportional to the strength of the applied field. We infer that all ballistic motion of electrons vanishes at a QCP, forming a new class of conductor in which individual 1 electrons decay into collective current carrying motions of the electron fluid.Recent work 6 on the heavy electron material YbRh 2 Si 2 9 has demonstrated that a magnetic field can be used to probe the heavy electron quantum critical point. This material exhibits a small antiferromagnetic (AFM) ordering temperature T N = 70 mK (Fig. 1a) that is driven to zero by a critical magnetic field B c = 0.66 T (if the field is applied parallel to the crystallographic c-axis, perpendicular to the easy magnetic plane) 6 . For 2 Past experience 7,8 suggested that a finite field quantum critical point has properties which are qualitatively different to a zero field transition, shedding doubt on the reliability of these measurements as an indicator of the physics of a quantum phase transition at zero field. However, the zero-field properties of YbRh 2 (Si 1−x Ge x ) 2 above T ≈ 70 mK for the undoped (x = 0) and doped (x = 0.05) crystals are essentially identical (Fig. 2a), suggesting that by suppressing the critical field we are still probing the same quantum critical point.In both compounds, the ac-susceptibility follows a temperature dependence χ −1 ∝ T α from 0.3 K to ≤ T ≤ 1.5 K, with α = 0.75 14 , and the coefficient of the electronic specific heat, C el (T )/T , exhibits 9 a logarithmic divergence between 0.3 K and 10 K. However, in the low-T paramagnetic regime, i. e. , T N < T < ∼ 0.3 K, the ac-susceptibility follows a CurieWeiss law (inset of Fig. 2a) with a Weiss temperature Θ W ≈ 0.3 K, and a surprisingly large effective moment µ eff ≈ 1.4µ B /Yb 3+ , indicating the emergence of coupled, unquenched spins at the quantum critical point. The electronic specific heat coefficient, C e...

Plastic is a broad name given to different polymers with high molecular weight, which can be degraded by various processes. However, considering their abundance in the environment and their specificity in attacking plastics, biodegradation of plastics by microorganisms and enzymes seems to be the most effective process. When plastics are used as substrates for microorganisms, evaluation of their biodegradability should not only be based on their chemical structure, but also on their physical properties (melting point, glass transition temperature, crystallinity, storage modulus etc.). In this review, microbial and enzymatic biodegradation of plastics and some factors that affect their biodegradability are discussed.

Poly(lactide) (PLA) has been developed and made commercially available in recent years. One of the major tasks to be taken before the widespread application of PLA is the fundamental understanding of its biodegradation mechanisms. This paper provides a short overview on the biodegradability and biodegradation of PLA. Emphasis is focused mainly on microbial and enzymatic degradation. Most of the PLA-degrading microorganisms phylogenetically belong to the family of Pseudonocardiaceae and related genera such as Amycolatopsis, Lentzea, Kibdelosporangium, Streptoalloteichus, and Saccharothrix. Several proteinous materials such as silk fibroin, elastin, gelatin, and some peptides and amino acids were found to stimulate the production of enzymes from PLA-degrading microorganisms. In addition to proteinase K from Tritirachium album, subtilisin, a microbial serine protease and some mammalian serine proteases such as alpha-chymotrypsin, trypsin, and elastase could also degrade PLA.

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Microbial polyhydroxyalkanoates (PHAs), one of the largest groups of thermoplastic polyesters are receiving much attention as biodegradable substitutes for non-degradable plastics. Poly(D-3-hydroxybutyrate) (PHB) is the most ubiquitous and most intensively studied PHA. Microorganisms degrading these polyesters are widely distributed in various environments. Although various PHB-degrading microorganisms and PHB depolymerases have been studied and characterized, there are still many groups of microorganisms and enzymes with varying properties awaiting various applications. Distributions of PHB-degrading microorganisms, factors affecting the biodegradability of PHB, and microbial and enzymatic degradation of PHB are discussed in this review. We also propose an application of a new isolated, thermophilic PHB-degrading microorganism, Streptomyces strain MG, for producing pure monomers of PHA and useful chemicals, including D-3-hydroxycarboxylic acids such as D-3-hydroxybutyric acid, by enzymatic degradation of PHB.