Pulsed ultraviolet light decontamination of artificially-generated microbiological aerosols

Airborne transmission of infectious organisms is a major public health concern, particularly within healthcare and communal public environments. Methods of environmental decontamination utilising pulsed ultraviolet (UV) light are currently available, however it is important that germicidal efficacy against airborne contamination is established. This study demonstrates evidence of the dose-response kinetics of airborne bacterial contamination when exposed to pulsed UV-rich (PUV) light. Bacterial aerosols (Staphylococcus epidermidis) were generated using a 6-Jet Collison nebuliser, and introduced into a custom-designed aerosol chamber which enabled prolonged airborne suspension and circulation. Bacterial aerosols were exposed to short duration pulses (~20 µs) of UV-rich light emitted from a xenon-filled flashlamp. The lamp was operated using a 1 kV solid–state pulsed power source, with a pulse frequency of 1 Hz, and output energy of 20 J/pulse. Post-treatment, air samples were extracted from the chamber using a BioSampler liquid impinger, and the surviving fraction was enumerated using standard microbiological culture methods. Results demonstrate successful aerosol inactivation, with a 66.4% reduction achieved with only 10 pulses of UV-rich light (P=<0.0002). Inactivation using continuous UV light was also investigated in order to quantify the comparative efficacy of these antimicrobial light regions. In addition to determining the inactivation kinetics, the spectral outputs of the pulsed and continuous UV sources were captured and compared in order to assess their comparative UV-C content, and subsequently assess how this UV content relates to their germicidal efficiency. Overall, results provide evidence of the dose-response kinetics of bacterial aerosols to PUV-rich light. As with continuous UV light, safety restrictions limit its application to unoccupied environments, or within sealed enclosures such as air handling units, however the reduced treatment times with PUV provides operational advantages over continuous light treatment

Pulsed ultraviolet light decontamination of artificially-generated microbiological aerosols

Airborne transmission of infectious organisms is a major public health concern, particularly within healthcare and communal public environments. Methods of environmental decontamination utilising pulsed ultraviolet (UV) light are currently available, however it is important that germicidal efficacy against airborne contamination is established. In this study bacterial aerosols were generated and exposed to short duration pulses (~20 µs) of UV-rich light emitted from a xenon-filled flashlamp. The lamp was operated using a 1 kV solid–state pulsed power source, with a pulse frequency of 1 Hz, and output energy of 20 J/pulse. Post-treatment, air samples were extracted from the chamber and the surviving fraction was enumerated using standard microbiological culture methods. Results demonstrate successful aerosol inactivation, with a 92.1% reduction achieved with only 5 pulses of UV-rich light (P=<0.0002). Inactivation using continuous UV light was also investigated in order to quantify the comparative efficacy of these antimicrobial light sources. Overall, results provide evidence of the comparative efficacy of pulsed and continuous UV light for inactivation of airborne bacterial contamination. For practical application, given the safety restrictions limiting its application for decontamination of unoccupied environments, or within sealed enclosures such as air handling units, the reduced treatment times with PUV provides significant operational advantages over continuous light treatment

Efficacy of Pulsed 405-nm LEDs for antimicrobial photodynamic inactivation : effects of intensity, frequency, and duty cycle

Objective: This study investigates possible advantages in pulsed over continuous 405-nm LED-light for bacterial inactivation and energy efficiency. Background: Alternative non-antibiotic methods of disinfection and infection control have become of significant interest. Recent studies have demonstrated the application of systems using 405-nm light-emitting diodes for continuous disinfection of the clinical environment, and also for potential treatment of contaminated wounds. Methods: Liquid suspensions of 103 CFU/ml populations of Staphylococcus aureus were subject to pulsed 405-nm light of different frequencies, duty cycles and intensities, and for different lengths of time. Results: Pulsed exposures with the same average irradiance of 16 mWcm2 and varying duty cycle (25%, 50%, 75%), showed very similar performance compared with continuous exposures, with 95-98% reduction of S. aureus achieved for all duty cycles. The pulsing frequency was varied in intervals from 100 Hz - 10 kHz and appeared to have little effect on antimicrobial efficacy. However, when comparing pulsed with continuous exposure, an improvement in inactivation per unit optical energy was achieved, with results showing an increase of approximately 83% in optical efficiency. Conclusions: These results suggest that under pulsed conditions a lower energy consumption and lower perceived brightness could be achieved, thus potentially providing improved operating conditions for medical/infection-control applications without compromising antimicrobial efficacy

ВЛИЯНИЕ ОБРАБОТКИ РАСПЛАВОВ ЭЛЕКТРОМАГНИТНЫМИ АКУСТИЧЕСКИМИ ПОЛЯМИ НА СТРУКТУРУ И СВОЙСТВА СПЛАВОВ СИСТЕМЫ Al–Si

The research on the influence of melt processing with electromagnetic acoustic fields on the structure and properties of binary alloys Al–12%Si and Al–20%Si was conducted. The frequency of electromagnetic field induced in the loop antenna was changed between 500, 1000 and 2000 kHz during the experiments. Melts were processed after their degassing and refining. It was determined that this method of melt processing reduces the average total time of alloy production by 12 %. Short-term treatment of melts with electromagnetic acoustic fields helps to grind main phase alloy components and to improve their mechanical properties. Grinding of α-Al dendrites (from 30 to 22 μm) and eutectic Si crystals (from 13 to 10 μm) was observed while processing Al–12%Si eutectic alloy with a frequency of 500 kHz. At the same time, Al–20%Si hypereutectic alloy treatment with a frequency of 1000 kHz led to reduction of eutectic Si crystals from 8 to 5 μm, and of primary Si crystals – from 90 to 62 μm. Under specified processing conditions the tensile strength of Al–12%Si eutectic alloy increased by 13 %, and elongation – by 17 %, the same mechanical properties of Al–20%Si hypereutectic alloy increased by 9 and 65 % respectively. Based on the studies performed it was concluded that the choice of parameters for Al–Si melt processing with electromagnetic acoustic fields depended on the silicon content in the alloy. The increase in silica concentration needs treatment with the waves of higher vibration frequency. This processing technique allows modifying the fine crystalline structure of alloys and as a result causes an improvement of their mechanical properties. It can be successfully used for the production of fine-grained ligatures and Al–Si system alloys. However, further research is required to determine optimal processing parameters depending on the structure of the original charge and the nature of the alloys.Выполнены исследования по влиянию обработки расплавов электромагнитными акустическими полями на структуру и свойства двойных сплавов Al–12%Si и Al–20%Si. В процессе экспериментов варьировали частоту электромагнитного поля, наводимого в петле-антенне: 500, 1000 и 2000 кГц. Обработку расплавов проводили после их дегазации и рафинирования. Установлено, что данный способ обработки расплавов обуславливает сокращение общего времени приготовления сплавов в среднем на 12 %. Кратковременная обработка расплавов электромагнитными акустическими полями способствует измельчению основных фазовых составляющих сплавов и повышению их механических свойств. При обработке эвтектического сплава Al–12%Si с частотой 500 кГц наблюдалось измельчение дендритов α-Al (с 30 до 22 мкм) и кристаллов эвтектического Si (с 13 до 10 мкм). При обработке заэвтектического сплава Al–20%Si с частотой 1000 кГц кристаллы эвтектического Si уменьшались с 8 до 5 мкм, первичного Si – с 90 до 62 мкм. При указанных режимах обработки эвтектического сплава Al–12%Si предел прочности при растяжении увеличился на 13 %, относительное удлинение – на 17 %; у заэвтектического сплава Al–20%Si те же показатели повысились на 9 и 65 % соответственно. На основании проведенных исследований сделан вывод о том, что выбор параметров обработки расплавов системы Al–Si электромагнитными акустическими полями должен обуславливаться содержанием кремния в сплаве. С увеличением концентрации кремния необходимо обрабатывать расплав волнами с большей частотой колебания. Указанный способ обработки позволяет получать модифицированную мелкокристаллическую структуру сплавов и, как следствие, вызывает повышение их механических свойств. Он может быть успешно использован при получении мелкокристаллических лигатур и в производстве сплавов системы Al–Si. Для определения оптимальных параметров обработки в зависимости от структуры исходной шихты и природы сплавов требуются дополнительные исследования

ВЛИЯНИЕ СТРУКТУРЫ ЛИГАТУРЫ AlSi20 НА МИКРОСТРУКТУРУ И ВЯЗКОСТЬ МОДЕЛЬНОГО СИЛУМИНА Al–6%Si В ТВЕРДОМ И ЖИДКОМ СОСТОЯНИЯХ

The effect of the structure of initial charging Al–20wt.%Si alloys on their structure after single remelting and crystallization at equal cooling rate of 20 °C/sec has been investigated. It is found that the structural information from initial charging alloys is steadily saved and transmitted in the «solid–liquid-solid» system. Viscosimetric study of the melts produced from large- and fine-crystalline charging alloys at heating to 1350 °С and subsequent cool-down has confirmed the conclusion that the melts are translators of the structural information. It is found that the temperature of viscosity polyterm branching (hysteresis) (th) at the conditions of heating and cool-down for the melt from coarse-crystalline charging alloy is 1100 °C and that from fine-crystalline charging alloy is 1000 °C. It is noted that in the second case and at cool-down lower than th the viscosity is characterized by elevated values and the polyterm branch has steeper climb. The obtained results testify in favor of using special procedures of charging metal processing for the purpose of embedding the positive structural information into them. Application of this approach is mostly expedient in producing aluminum based foundry alloys.Исследовано влияние структуры исходных шихтовых сплавов Al–20мас.%Si на их структуру после однократного переплава и кристаллизации с одинаковой скоростью охлаждения 20 °С/с. Установлено, что структурная информация от исходных шихтовых сплавов устойчиво сохраняется и транслируется в системе «твердое–жидкое–твердое». Вискозиметрическое изучение расплавов, полученных из крупно- и мелкокристаллических шихтовых сплавов в режиме нагрева до 1350 °С и последующего охлаждения, подтвердило вывод о том, то расплавы являются трансляторами структурной информации. Установлено, что температура ветвления (гистерезис) политерм вязкости (tг) в режимах нагрева и охлаждения для расплава из крупнокристаллического шихтового сплава составляет 1100 °С, а из мелкокристаллического шихтового сплава – 1000 °С. Отмечено, что во втором случае вязкость в режиме охлаждения ниже tг характеризуется повышенными значениями, а ветвь политермы имеет более крутое восхождение. Полученные результаты свидетельствуют в пользу использования специальных способов обработки шихтовых металлов с целью закладки в них положительной структурной информации. Применение данного подхода наиболее целесообразно при получении лигатур на основе алюминия.

Rapid ecological change in the coastal zone of Lake Baikal (East Siberia): Is the site of the world\u27s greatest freshwater biodiversity in danger?

Ecological degradation of the benthic littoral zone is an emerging, urgent problem at Lake Baikal (East Siberia), the most species-rich lake on Earth. Within the last five years, multiple changes have occurred in the nearshore benthos where most of the lake\u27s endemic species reside. These changes include proliferation of benthic algae, deaths of snails and endemic sponges, large coastal wash-ups of dead benthic algae and macrophytes, blooms of toxin-producing benthic cyanobacteria, and inputs of industrial contaminants into parts of the lake. Some changes, such as massive coastal accumulations of benthic algae, are currently shared with the Laurentian Great Lakes (LGLs); however, the drivers of these changes differ between Lake Baikal and the LGLs. Coastal eutrophication from inputs of untreated sewage is causing problems at multiple sites in Lake Baikal, whereas in the LGLs, invasive dreissenid mussels redirect pelagic nutrients to the littoral substrate. At other locations in Lake Baikal, ecological degradation may have different causes including water level fluctuations and the input of toxic industrial contaminants. Importantly, the recent deterioration of the benthic littoral zone in both Lake Baikal and the LGLs has occurred while little change has occurred offshore. This highlights the necessity of monitoring both the littoral and pelagic zones of large lakes for assessing ecosystem health, change and conservation

A FRW Dark Fluid with a Non-Linear Inhomogeneous Equation of State

A dark Friedman-Robertson-Walker fluid governed by a non-linear inhomogeneous equation of state is considered which can be viewed as a conveniently simple paradigm for a whole class of models which exhibit phase transitions from a non-phantom towards a phantom era (superacceleration transition). From another side, such dark fluid models may describe also quintessence-like cosmic acceleration. Thermodynamical considerations for the processes involved, which are of great importance in the characterization of the global evolution of the corresponding universe, are given too. Connecting the proposed equation of state with an anisotropic Kasner universe with viscosity, we are led to the plausible conjecture of a dark fluid origin of the anisotropies in the early universe.Comment: 11 pages pdf, 2 figures; to appear in Eur. Phys. J.