1,014 research outputs found
Computer vision approach for the determination of microbial concentration and growth kinetics using a low cost sensor system
The measurement of microbial contamination is of primary importance in different fields, from environmental monitoring to food safety and clinical analysis. Today, almost all microbiology laboratories make microbial concentration measurements using the standard Plate Count Technique (PCT), a manual method that must be performed by trained personnel. Since manual PCT analysis can result in eye fatigue and errors, in particular when hundreds of samples are processed every day, automatic colony counters have been built and are commercially available. While quick and reliable, these instruments are generally expensive, thus, portable colony counters based on smartphones have been developed and are of low cost but also not accurate as the commercial benchtop instruments. In this paper, a novel computer vision sensor system is presented that can measure the microbial concentration of a sample under test and also estimate the microbial growth kinetics by monitoring the colonies grown on a Petri dish at regular time intervals. The proposed method has been in-house validated by performing PCT analysis in parallel under the same conditions and using these results as a reference. All the measurements have been carried out in a laboratory using benchtop instruments, however, such a system can also be realized as an embedded sensor system to be deployed for microbial analysis outside a laboratory environment
Rigorous derivation of coherent resonant tunneling time and velocity in finite periodic systems
The velocity of resonant tunneling electrons in finite periodic
structures is analytically calculated in two ways. The first method is based on
the fact that a transmission of unity leads to a coincidence of all still
competing tunneling time definitions. Thus, having an indisputable resonant
tunneling time we apply the natural definition
to calculate the velocity. For the second method we
combine Bloch's theorem with the transfer matrix approach to decompose the wave
function into two Bloch waves. Then the expectation value of the velocity is
calculated. Both different approaches lead to the same result, showing their
physical equivalence. The obtained resonant tunneling velocity is
smaller or equal to the group velocity times the magnitude of the complex
transmission amplitude of the unit cell. Only at energies where the unit cell
of the periodic structure has a transmission of unity equals the
group velocity. Numerical calculations for a GaAs/AlGaAs superlattice are
performed. For typical parameters the resonant velocity is below one third of
the group velocity.Comment: 12 pages, 3 figures, LaTe
Neutron spectrometer for fast nuclear reactors
In this paper we describe the development and first tests of a neutron
spectrometer designed for high flux environments, such as the ones found in
fast nuclear reactors. The spectrometer is based on the conversion of neutrons
impinging on Li into and whose total energy comprises the
initial neutron energy and the reaction -value. The LiF layer is
sandwiched between two CVD diamond detectors, which measure the two reaction
products in coincidence. The spectrometer was calibrated at two neutron
energies in well known thermal and 3 MeV neutron fluxes. The measured neutron
detection efficiency varies from 4.2 to 3.5 for
thermal and 3 MeV neutrons, respectively. These values are in agreement with
Geant4 simulations and close to simple estimates based on the knowledge of the
Li(n,) cross section. The energy resolution of the spectrometer
was found to be better than 100 keV when using 5 m cables between the detector
and the preamplifiers.Comment: submitted to NI
Leading and higher twists in the proton polarized structure function at large Bjorken x
A phenomenological parameterization of the proton polarized structure
function has been developed for x > 0.02 using deep inelastic data up to ~ 50
(GeV/c)**2 as well as available experimental results on both photo- and
electro-production of proton resonances. According to the new parameterization
the generalized Drell-Hearn-Gerasimov sum rule is predicted to have a
zero-crossing point at Q**2 = 0.16 +/- 0.04 (GeV/c)**2. Then, low-order
polarized Nachtmann moments have been estimated and their Q**2-behavior has
been investigated in terms of leading and higher twists for Q**2 > 1
(GeV/c)**2. The leading twist has been treated at NLO in the strong coupling
constant and the effects of higher orders of the perturbative series have been
estimated using soft-gluon resummation techniques. In case of the first moment
higher-twist effects are found to be quite small for Q**2 > 1 (GeV/c)**2, and
the singlet axial charge has been determined to be a0[10 (GeV/c)**2] = 0.16 +/-
0.09. In case of higher order moments, which are sensitive to the large-x
region, higher-twist effects are significantly reduced by the introduction of
soft gluon contributions, but they are still relevant at Q**2 ~ few (GeV/c)**2
at variance with the case of the unpolarized transverse structure function of
the proton. Our finding suggests that spin-dependent correlations among partons
may have more impact than spin-independent ones. As a byproduct, it is also
shown that the Bloom-Gilman local duality is strongly violated in the region of
polarized electroproduction of the Delta(1232) resonance.Comment: revised version to appear in Phys. Rev. D; extended discussion on the
generalized DHG sum rul
Outcomes after open and endovascular repair of non-ruptured true pancreaticoduodenal and gastroduodenal artery aneurysms associated with coeliac artery compression. A multicentre retrospective study
Objective: True aneurysms of the peri-pancreatic arcade (PDAA) have been attributed to increased collateral flow related to coeliac axis (CA) occlusion by a median arcuate ligament (MAL). Although PDAA exclusion is currently recommended, simultaneous CA release and the technique to be used are debated. The aim of this retrospective multicentre study was to compare the results of open surgical repair of true non-ruptured PDAA with release or CA bypass (group A) vs. coil embolisation of PDAA and CA stenting or laparoscopic release (group B). Methods: From January 1994 to February 2019, 57 consecutive patients (group A: 31 patients; group B: 26 patients), including 35 (61%) men (mean age 56 ± 11 years), were treated at three centres. Twenty-six patients (46%) presented with non-specific abdominal pain: 15 (48%) in group A and 11 (42%) in group B (p = .80). Results: No patient died during the post-operative period. At 30 days, all PDAAs following open repair and embolisation had been treated successfully. In group A, all CAs treated by MAL release or bypass were patent. In group B, 2/12 CA stentings failed at < 48 hours, and all MAL released by laparoscopy were successful. Median length of hospital stay was significantly greater in group A than in group B (5 vs. 3 days; p = .001). In group A, all PDAAs remained excluded. In group B, three PDAA recanalisations following embolisation were treated successfully (two redo embolisations and one open surgical resection). At six years, Kaplan–Meier estimates of freedom for PDAA recanalisation were 100% in group A, and 88% ± 6% in group B (p = .082). No PDAA ruptured during follow up. In group A, all 37 CAs treated by MAL release were patent, and one aortohepatic bypass occluded. In group B, five CAs occluded: four after stenting and the other after laparoscopic MAL release with two redo stenting and three aortohepatic bypasses. Estimates of freedom from CA restenosis/occlusion were 95% ± 3% for MAL release or visceral bypass, and 60% ± 9% for CA stenting (p = .001). Two late restenoses following CA stenting were associated with PDAA recanalisation. Conclusion: Current data suggest that open and endovascular treatment of PDAA can be performed with excellent post-operative results in both groups. However, PDAA embolisation was associated with few midterm recanalisations and CA stenting with a significant number of early and midterm failures
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