Prisutnost bakterija u zraku nastambi za svinje i neposrednom okolišu

This paper describes a bacteriological analysis of air samples taken from swine housing facilities and the immediate environment. The air volume of the samples was pre-programmed by a standard air sampler (MAS-100, Merck) and was directly impacted onto the bacteriologic agar surface (Petri dishes, standard diameter of 90 mm). The bacterial contamination in forty-eight samples was 2.59x105 CFU/m3 (ranging from 8.46x104 to 5.30x105 CFU/m3). Potentially pathogenic bacterial agents predominated in all samples (100%), while primarily pathogenic bacteria were isolated in a minor proportion of samples (33%–66%). Airborne bacterial contamination in samples (N=16) obtained from emptied facilities ranged from 1.8x103 CFU/m3 (that is, after coarse mechanical washing) to 0.8x102 CFU/m3 (upon completion of disinfection). Control measurements at different locations and distance from the farm (N=32) pointed to the presence of non-pathogenic airborne bacteria, ranging from 1.55x102 to 3.70x102 CFU/m3. The results of this preliminary study showed that the emission of potentially pathogenic bacteria from animal housing facilities to the immediate farm environment via aerosol was very low.Pored kontrole emisija štetnih plinova, vlage i čestica prašine u nastambama za životinje, važna je i detekcija ukupne bakterijske kontaminacije zraka. Od posebnog su značenja i moguće emisije u okoliš, osobito potencijalno ili primarno patogenih bakterija. U raspravi su prikazani rezultati prvih istraživanja bakterijske kontaminacije zraka u nastambama, kao i u neposrednom okolišu provedenih na jednoj farmi svinja. Programirani volumen zraka standardnim je skupljačem zraka (MAS-100-Merck) direktno naslojen na površine bakterioloških podloga (Petrijeve ploče promjera 90 mm). U pretraženih 48 uzoraka u nastambama ustanovljena je prosječna bakterijska kontaminacija zraka za farmu od 2,595 CFU/m3 (od 8,464 do 5,305). U svim su uzorcima dominantno bili prisutni Streptococcus spp., Micrococcus spp., Escherichia coli, Staphylococcus aureus i Streptococcus suis. U manjem broju uzoraka izdvojeni su potencijalno patogeni uzročnici Pasteurella multocida (66%), Actinobacillus suis (50%), hemolitični sojevi E. coli (41%) te Pasteurella haemolytica, Bordetella bronchiseptica i Actinobacillus pleuropneumoniae (33%). Mjerenjima u praznim objektima, prije useljenja životinja (16 uzoraka), ustanovljena je srednja kontaminacija zraka od 9,01 do 0,41 CFU/m3 s bakterijskim uzročnicima Streptococcus spp., Staphylococcus spp. i E. coli. Kontrolna mjerenja izvan objekata (32 uzorka) upozorila su na prosječnu kontaminaciju zraka od 0,261 CFU/m3 (od 0,151 do 0,371) i uz zastupljenost apatogenih uzročnika Bacillus subtilis, Bacillus cereus, E. coli, Streptococcus spp., Micrococcus spp. i Staphylococcus spp. Rezultati pokazuju da su neznatne emisije potencijalno patogenih bakterijskih uzročnika putem aerosola iz nastambi za svinje u neposredni okoliš. Unatoč sve sofisticiranijim uređajima za monitoring, ni danas još, u okviru programa animalne higijene, nisu određene granične vrijednosti za bakteriološku kontaminaciju zraka kao što je to slučaj s emisijom štetnih plinova NH3 i CO2

Time-of-Flight Measurements of Single-Electron Wave Packets in Quantum Hall Edge States.

We report time-of-flight measurements on electrons traveling in quantum Hall edge states. Hot-electron wave packets are emitted one per cycle into edge states formed along a depleted sample boundary. The electron arrival time is detected by driving a detector barrier with a square wave that acts as a shutter. By adding an extra path using a deflection barrier, we measure a delay in the arrival time, from which the edge-state velocity v is deduced. We find that v follows 1/B dependence, in good agreement with the E[over →]×B[over →] drift. The edge potential is estimated from the energy dependence of v using a harmonic approximation.UK Department for Business, Innovation and SkillsThis is the author accepted manuscript. The final version is available from the American Physical Society via http://dx.doi.org/10.1103/PhysRevLett.116.12680

Measurement and control of electron wave packets from a single-electron source

We report an experimental technique to measure and manipulate the arrival-time and energy distributions of electrons emitted from a semiconductor electron pump, operated as both a singleelectron source and a two-electron source. Using an energy-selective detector whose transmission we control on picosecond time scales, we can measure directly the electron arrival-time distribution and we determine the upper bound to the distribution width to be 30 ps. We study the effects of modifying the shape of the voltage waveform that drives the electron pump, and show that our results can be explained by a tunneling model of the emission mechanism. This information was in turn used to control the emission-time difference and energy gap between a pair of electrons.This research was supported by the UK Department for Business, Innovation and Skills, the National Physical Laboratory’s Strategic Research Programme and the UK Engineering and Physical Sciences Research Council. V.K. has been supported by the Latvian Council of Science within research project no. 146/2012.This is the author accepted manuscript. The final version is available from APS via http://dx.doi.org/10.1103/PhysRevB.92.12530

LO-Phonon Emission Rate of Hot Electrons from an On-Demand Single-Electron Source in a GaAs/AlGaAs Heterostructure.

Using a recent time-of-flight measurement technique with 1 ps time resolution and electron-energy spectroscopy, we develop a method to measure the longitudinal-optical-phonon emission rate of hot electrons traveling along a depleted edge of a quantum Hall bar. Comparison to a single-particle model implies the scattering mechanism involves a two-step process via an intra-Landau-level transition. We show that this can be suppressed by control of the edge potential profile, and a scattering length >1  mm can be achieved, allowing the use of this system for scalable single-electron device applications

Weak localization scattering lengths in epitaxial, and CVD graphene

Weak localization in graphene is studied as a function of carrier density in the range from 1 x 10(11) cm(-2) to 1.43 x 10(13) cm(-2) using devices produced by epitaxial growth onto SiC and CVD growth on thin metal film. The magnetic field dependent weak localization is found to be well fitted by theory, which is then used to analyze the dependence of the scattering lengths L-phi, L-i, and L-* on carrier density. We find no significant carrier dependence for L-phi, a weak decrease for L-i with increasing carrier density just beyond a large standard error, and a n(-1/4) dependence for L-*. We demonstrate that currents as low as 0.01 nA are required in smaller devices to avoid hot-electron artifacts in measurements of the quantum corrections to conductivity

Towards a quantum representation of the ampere using single electron pumps

Electron pumps generate a macroscopic electric current by controlled manipulation of single electrons. Despite intensive research towards a quantum current standard over the last 25 years, making a fast and accurate quantised electron pump has proved extremely difficult. Here we demonstrate that the accuracy of a semiconductor quantum dot pump can be dramatically improved by using specially designed gate drive waveforms. Our pump can generate a current of up to 150 pA, corresponding to almost a billion electrons per second, with an experimentally demonstrated current accuracy better than 1.2 parts per million (ppm) and strong evidence, based on fitting data to a model, that the true accuracy is approaching 0.01 ppm. This type of pump is a promising candidate for further development as a realisation of the SI base unit ampere, following a re-definition of the ampere in terms of a fixed value of the elementary charge.Comment: 8 pages, 7 figure

Breakdown of the quantum Hall effect in epitaxial graphene

We present the phase space defined by the quantum Hall effect breakdown in polymer gated epitaxial graphene on SiC (SiC/G) as a function of temperature, current, carrier density, and magnetic field. At 2 K, breakdown currents (Ic) almost 2 orders of magnitude greater than in GaAs devices are observed. We use this knowledge to explore the potential of using graphene as a high temperature (> 2 K) and low magnetic field (< 5 T) quantum resistance standard