Rate of Homogeneous Crystal Nucleation in molten NaCl

We report a numerical simulation of the rate of crystal nucleation of sodium chloride from its melt at moderate supercooling. In this regime nucleation is too slow to be studied with "brute-force" Molecular Dynamics simulations. The melting temperature of ("Tosi-Fumi") NaCl is $\sim 1060$K. We studied crystal nucleation at $T$=800K and 825K. We observe that the critical nucleus formed during the nucleation process has the crystal structure of bulk NaCl. Interestingly, the critical nucleus is clearly faceted: the nuclei have a cubical shape. We have computed the crystal-nucleation rate using two completely different approaches, one based on an estimate of the rate of diffusive crossing of the nucleation barrier, the other based on the Forward Flux Sampling and Transition Interface Sampling (FFS-TIS) methods. We find that the two methods yield the same result to within an order of magnitude. However, when we compare the extrapolated simulation data with the only available experimental results for NaCl nucleation, we observe a discrepancy of nearly 5 orders of magnitude. We discuss the possible causes for this discrepancy

Hospital environment as a reservoir for cross transmission. Cleaning and disinfection procedures

Background. Healthcare associated infections (HAIs) represent a serious problem for public health, as they increase the morbidity and mortality rates, present a relevant financial burden, and significantly contribute to the antimicrobial resistance. Methods. The aim of this review was to investigate the literature about HAIs, with particular reference to hospital environments and the role of cleaning and disinfection procedures. Hospital environments are an essential reservoir for HAIs cross transmission, and the application of appropriate procedures related to hand hygiene and disinfection/sterilization of surfaces and instruments remain key strategies for controlling HAIs. Results. Different procedures, based on the risk associated with the healthcare procedure, are recommended for hand hygiene: washing with soap and water, antiseptic rubbing with alcohol-based disinfectants, antiseptic and surgical hand washing. Environmental surfaces can be treated with different products, and the mostly used are chlorine-based and polyphenolic disinfectant. The reprocessing of instruments is related to their use according to the Spaulding's classification. In addition, scientific evidence demonstrated the great relevance of the "bundles" (small set of practices performed together) in controlling HAIs. Conclusions. Research agenda should include the improvement of well-known effective preventive procedures and the development of new bundles devoted to high-risk procedures and specific microorganisms

Non-equilibrium dynamics of an active colloidal "chucker"

We report Monte Carlo simulations of the dynamics of a "chucker": a colloidal particle which emits smaller solute particles from its surface, isotropically and at a constant rate k_c. We find that the diffusion constant of the chucker increases for small k_c, as recently predicted theoretically. At large k_c the chucker diffuses more slowly due to crowding effects. We compare our simulation results to those of a "point particle" Langevin dynamics scheme in which the solute concentration field is calculated analytically, and in which hydrodynamic effects can be included albeit in an approximate way. By simulating the dragging of a chucker, we obtain an estimate of its apparent mobility coefficient which violates the fluctuation-dissipation theorem. We also characterise the probability density profile for a chucker which sediments onto a surface which either repels or absorbs the solute particles, and find that the steady state distributions are very different in the two cases. Our simulations are inspired by the biological example of exopolysaccharide-producing bacteria, as well as by recent experimental, simulation and theoretical work on phoretic colloidal "swimmers".Comment: re-submission after referee's comment

Explicit and tacit knowledge in construction of passive housing, knowledge models in Lithuania / Išreikštinės ir neišreikštinės žinios pasyviųjų namų statyboje, žinių modeliai pasaulyje ir Lietuvoje

Optimization of building maintenance expenditure becomes really an urgent issue in Lithuania. People prefer a warmer housing and show interest in recent decisions of engineering systems. They are looking for the best decision of heating costs optimization to price down heating costs not 10-20%, but a number of times. The results of passive houses scientific research as well as models of passive housing are discussed in the article. They ascertain and compare features of passive housing construction in different countries which depends on climatic conditions. Most countries support traditional housing. Remarkable thermal resistance and cost efficient maintenance of passive housing may be reached through an integrated approach of using proper architectural, constructional and engineering resolution, as well as applying the most relevant material usage and elaborating and accumulating practical knowledge. Lithuania, as well as other countries in the world, reveals that the concept of tacit knowledge still lacks sufficient attention within the construction industry, despite the fact that proper understanding and management of this resource is of immense importance for the achievement of better organizational performance. As the initial step towards the management of tacit knowledge, this paper examines the factors affecting tacit knowledge generation and utilization in the construction industry. Santrauka Lietuvoje ypač aktualus tampa pastato eksploatacinių išlaidų optimizavimas. Žmonės renkasi šiltesnį būstą, domisi naujausiais inžinerinių sistemų sprendimais. Išlaidų šildymui sumažinti ne 10–20 %, bet bent kelis kartus, ieškomas geriausias šildymo išlaidų optimizavimo būdas. Straipsnyje aptarti pasaulyje atlikti pasyvaus būsto moksliniai tyrimai, bei pasyvaus namo modeliai. Išaiškinti ir palyginti įvairių šalių pasyvių namų statybos ypatumai, priklausomai nuo klimato sąlygų. Daugelyje šalių yra palaikomos ankstesnės statybų tradicijos. Puikių pasyviojo namo šiluminės varžos ir ekonomiškumo rezultatų galima pasiekti kompleksiškai taikant optimalius architektūrinius, statybinius ir inžinerinius sprendimus, siekti geresnių medžiagų panaudojimo, tobulinti ir kaupti praktikos įgūdžius statyboje. Jei rinkos sąlygos leidžia, turimas žinias reikia struktūrinti. Pastebima, kad Lietuvoje ir pasaulyje statybos pramonės viduje išreikštinių ir neišreikštinių žinių sąvokos vis dar stokoja pakankamo dėmesio, neatsižvelgiant į tai, kad tinkamas supratimas ir turimų išteklių vadyba turi didžiulę reikšmę siekiant geresnių tendencijų projektavime, o taip pat neišreikštų žinių generavime ir panaudojime statyboje. Raktiniai žodžiai: pasyvusis būstas, išreikštinės žinios, neišreikštinės žinios, energijos taupyma