Targeted disruption of the mouse transforming growth factor-beta 1 gene results in multifocal inflammatory disease.

Transforming growth factor-beta 1 (TGF-beta 1) is a multifunctional growth factor that has profound regulatory effects on many developmental and physiological processes. Disruption of the TGF-beta 1 gene by homologous recombination in murine embryonic stem cells enables mice to be generated that carry the disrupted allele. Animals homozygous for the mutated TGF-beta 1 allele show no gross developmental abnormalities, but about 20 days after birth they succumb to a wasting syndrome accompanied by a multifocal, mixed inflammatory cell response and tissue necrosis, leading to organ failure and death. TGF-beta 1-deficient mice may be valuable models for human immune and inflammatory disorders, including autoimmune diseases, transplant rejection and graft versus host reactions.     

Ni2MnGa铁磁形状记忆材料

铁磁形状记忆合金 (FSMA)是在一定温度范围马氏体相稳定同时又具铁磁性的一类特殊的形状记忆合金。Ni2MnGa铁磁形状记忆合金近年来成为呈现磁场驱动大应变的新型驱动材料 ,这些应变来自磁场诱发马氏体孪晶的重排 ,而不是磁场对奥氏体至马氏体相变的作用。孪晶变体的重排在宏观上呈现为正或切应变 ,一非化学计量比Ni2 MnGa单晶于室温加 0 .4T磁场能产生6 %的应变 ,Ni Mn Ga单晶在高至 15 0Hz的交变磁场仍可得到 2 .5 %的应变。本文阐述了与这种磁控形状记忆效应相关的孪晶界迁动的磁学和晶体学理论。马氏体相的大磁晶各向异性能使磁化沿c轴方向有利 ,穿过孪晶界c轴刚好转动 90度 ,同时 ,这个孪晶界也构成了约 90度的畴界。在各向异性的情况下 ,孪晶界的迁动仅有相邻孪晶变体的Zeeman能差驱动 ,μ0 ΔMis·Hi。磁场和外应力对应变的影响通过对一简单的自由能表达式取极小值来表示 ,自由能表达式包括Zeeman能、磁晶各向异性能和外应力以及在某些情况下需考虑的内部弹性能 ,模型的所有参数可通过应力 应变曲线和磁化曲线测量得到。铁磁形状记忆合金的磁场诱发应变可类比传统热弹性形状记忆效应 ,与更为人们所熟知的磁致伸缩现象不同。     

Expanding the diversity of chemical protein modification allows post-translational mimicry

One of the most important current scientific paradoxes is the economy with which nature uses genes. In all higher animals studied, we have found many fewer genes than we would have previously expected. The functional outputs of the eventual products of genes seem to be far more complex than the more restricted blueprint. In higher organisms, the functions of many proteins are modulated by post-translational modifications (PTMs). These alterations of amino-acid side chains lead to higher structural and functional protein diversity and are, therefore, a leading contender for an explanation for this seeming incongruity. Natural protein production methods typically produce PTM mixtures within which function is difficult to dissect or control. Until now it has not been possible to access pure mimics of complex PTMs. Here we report a chemical tagging approach that enables the attachment of multiple modifications to bacterially expressed (bare) protein scaffolds: this approach allows reconstitution of functionally effective mimics of higher organism PTMs. By attaching appropriate modifications at suitable distances in the widely-used LacZ reporter enzyme scaffold, we created protein probes that included sensitive systems for detection of mammalian brain inflammation and disease. Through target synthesis of the desired modification, chemistry provides a structural precision and an ability to retool with a chosen PTM in a manner not available to other approaches. In this way, combining chemical control of PTM with readily available protein scaffolds provides a systematic platform for creating probes of protein-PTM interactions. We therefore anticipate that this ability to build model systems will allow some of this gene product complexity to be dissected, with the aim of eventually being able to completely duplicate the patterns of a particular protein's PTMs from an in vivo assay into an in vitro system.     

Controlled exchange interaction between pairs of neutral atoms in an optical lattice

Ultracold atoms trapped by light offer robust quantum coherence and controllability, providing an attractive system for quantum information processing and for the simulation of complex problems in condensed matter physics. Many quantum information processing schemes require the manipulation and deterministic entanglement of individual qubits; this would typically be accomplished using controlled, state-dependent, coherent interactions among qubits. Recent experiments have made progress towards this goal by demonstrating entanglement among an ensemble of atoms confined in an optical lattice. Until now, however, there has been no demonstration of a key operation: controlled entanglement between atoms in isolated pairs. Here we use an optical lattice of double-well potentials to isolate and manipulate arrays of paired (87)Rb atoms, inducing controlled entangling interactions within each pair. Our experiment realizes proposals to use controlled exchange coupling in a system of neutral atoms. Although 87Rb atoms have nearly state-independent interactions, when we force two atoms into the same physical location, the wavefunction exchange symmetry of these identical bosons leads to state-dependent dynamics. We observe repeated interchange of spin between atoms occupying different vibrational levels, with a coherence time of more than ten milliseconds. This observation demonstrates the essential component of a neutral atom quantum SWAP gate (which interchanges the state of two qubits). Its 'half-implementation', the root SWAP gate, is entangling, and together with single-qubit rotations it forms a set of universal gates for quantum computation.