Characterizing pathological imperfections in macromolecular crystals: lattice disorders and modulations

Macromolecular crystal structure determination can be complicated or brought to a halt by crystal imperfections. These issues motivated us to write up what we affectionately call ‘The Definitive Hitchhiker’s Guide to Pathological Macromolecular Crystals: Lattice Disorders and Modulations’. Perhaps the most challenging imperfections are lattice order–disorder phenomena and positional modulations. Many of these types of crystals have been solved, and progress has been made on the more challenging forms. Diagnostic tools and how to solve many of these problem crystal structures are reviewed. New avenues are provided for approaching the solution of incommensurately modulated crystals. There are a good number of case studies in the literature of lattice order–disorder phenomena and crystallographic modulations that make it timely to write a review. This review concludes with a projected pathway for solving incommensurately modulated crystals, personal views of future directions and needs of the crystallographic community.     

路堤饱和软土地基初始孔压分布及沉降分析

变形和稳定性问题是岩土工程中需要解决的两个主要问题，尤其是在软土地基上修建公路，这两个问题就更加突出。从工程实用角度出发，将饱和软土地基视为Biot介质，假定路堤荷载瞬时施加，求得了地基中初始超静孔隙水压力的分布，以及有效应力的分布，进一步求得瞬时沉降和固结沉降。分析了压缩层厚度和土骨架泊松比对瞬时沉降和固结沉降的影响，为施工前填土方量计算、填筑结束后地基超静孔隙水压力分布和沉降计算提供了依据，其计算表达式简洁，便于工程应用。最后对一个工程实例进行了分析。     

浅谈斜面结构混凝土施工

结合具体工程实例，对混凝土斜面结构施工中可能出现的露筋、露石、蜂窝、气泡等缺陷进行了分析，从保证混凝土和易性、控制坍落度等方面，提出了避免缺陷发生所应采取的相应措施。     

人工挖孔桩施工技术探讨

通过对人工挖孔桩施工技术探讨,阐明了人工挖孔桩施工质量控制以及安全控制要点。     

Defects in offsite construction: timber module prefabrication

The construction industry is based on craftsmanship. Quality control and assurance procedures applied in manufacturing cannot usually be readily applied in construction, where there are higher degrees of uniqueness in each project. One category of companies, industrialized housebuilders, is attempting to bridge some of the gaps between construction and manufacturing. These companies prefabricate building modules for later assembly at the building site. Since they are wholly responsible for large parts of the building process, these companies have greater opportunities to control and improve quality in a more consistent way than ordinary construction companies. Thus, it could be hypothesized that the frequency and severity of defects should be lower in industrialized housing than in ordinary construction. The aim of the study presented here is to examine this hypothesis by measuring and characterizing defects in industrialized housing. The design and manufacturing processes at two Swedish timber module prefabrication firms has been analysed through interviews, site visits and document reviews. Quality audits from three phases of the building process were compiled, analysed and categorized to provide statistical measures of defects in industrialized housing. The results show that the case study companies are better in terms of product quality than conventional housing.     

掺合料对低温混凝土孔径分布的影响

目的 针对低温条件下东北地区施工特点,研究了在不掺防冻剂的情况下,不同掺合料对C30幼龄期混凝土孔径分布的影响.方法：采用压汞法测试了在恒低温一次冻结和自然变低温多次冻结养护情况下幼龄期混凝土的孔径分布情况.结论：掺合料可以改善低温混凝土的内部结构,减少多害孔和有害孔的比例,提高少害孔和无害孔的比例;混凝土在恒低温-10℃养护条件下较之变低温-15℃～5℃养护条件下有害孔和多害孔所占比例高,少害孔和无害孔所占比例低.     

Origin of extrinsic dielectric loss in 1:2 ordered,single-phase BaMg1/3Ta2/3O3

Among the family of temperature-compensated microwave dielectric ceramics, BaMg_1/3Ta_2/3O₃ shows the lowest dielectric loss and remains a material of choice for state-of-the-art airborne and land-based communication systems. We report on the compositional stability range, microwave dielectric properties, and the degree of atomic order of the title compound within the BaO–MgO–Ta₂O₅ ternary diagram. In most cases an atomic order is robust to the deviation from stoichiometry with an exception of Ba-rich and/or Ta-deficient samples which favor (partial) disorder. We further demonstrate that the dense, atomically ordered BaMg_1/3Ta_2/3O₃ ceramic shows large variation of dielectric loss within a single phase composition region – a clear message that the dielectric loss in practical ceramics is dominated by extrinsic sources and that the cation order alone is insufficient to achieve a minimum dielectric loss in BaMg_1/3Ta_2/3O₃. The low-temperature dielectric relaxation studies suggest that the extrinsic dielectric loss in the title compound is due to the ‘rattling’ of the off-centered Mg²⁺ ions misplaced at the Ba sites. Controlled deviation from the BaMg_1/3Ta_2/3O₃ stoichiometry toward the Mg-deficient region leads to suppression of the extrinsic dielectric loss as a result of the reduced chemical activity of Mg ion.     

Postconditioning by Delayed Administration of Ciclosporin A: Implication for Donation after Circulatory Death (DCD)

Heart transplantation is facing a shortage of grafts. Donation after Circulatory Death (DCD) would constitute a new potential of available organs. In the present work, we aimed to evaluate whether Postconditioning (ischemic or with ciclosporin-A (CsA)) could reduce ischemia-reperfusion injury in a cardiac arrest model when applied at the start of reperfusion or after a delay. An isolated rat heart model was used as a model of DCD. Hearts were submitted to a cardiac arrest of 40 min of global warm ischemia (37 °C) followed by 3 h of 4 °C-cold preservation, then 60 min reperfusion. Hearts were randomly allocated into the following groups: control, ischemic postconditioning (POST, consisting of two episodes each of 30 s ischemia and 30 s reperfusion at the onset of reperfusion), and CsA group (CsA was perfused at 250 nM for 10 min at reperfusion). In respective subgroups, POST and CsA were applied after a delay of 3, 10, and 20 min. Necrosis was lower in CsA and POST versus controls (p < 0.01) whereas heart functions were improved (p < 0.01). However, while the POST lost its efficacy if delayed beyond 3 min of reperfusion, CsA treatment surprisingly showed a reduction of necrosis even if applied after a delay of 3 and 10 min of reperfusion (p < 0.01). This cardioprotection by delayed CsA application correlated with better functional recovery and higher mitochondrial respiratory index. Furthermore, calcium overload necessary to induce mitochondrial permeability transition pore (MPTP) opening was similar in all cardioprotection groups, suggesting a crucial role of MPTP in this delayed protection of DCD hearts.     

Triplin: Functional Probing of Its Structure and the Dynamics of the Voltage-Gating Process

Gram-negative bacteria have a large variety of channel-forming proteins in their outer membrane, generally referred to as porins. Some display weak voltage dependence. A similar trimeric channel former, named Triplin, displays very steep voltage dependence, rivaling that responsible for the electrical excitability of mammals, and high inter-subunit cooperativity. We report detailed insights into the molecular basis for these very unusual properties explored at the single-molecule level. By using chemical modification to reduce the charge on the voltage sensors, they were shown to be positively charged structures. Trypsin cleavage of the sensor eliminates voltage gating by cleaving the sensor. From asymmetrical addition of these reagents, the positively charged voltage sensors translocate across the membrane and are, thus, responsible energetically for the steep voltage dependence. A mechanism underlying the cooperativity was also identified. Theoretical calculations indicate that the charge on the voltage sensor can explain the rectification of the current flowing through the open pores if it is located near the pore mouth in the open state. All results support the hypothesis that one of the three subunits is oriented in a direction opposite to that of the other two. These properties make Triplin perhaps the most complex pore-forming molecular machine described to date.