168 research outputs found
Bacteria colonies modify their shear and compressive mechanical properties in response to different growth substrates
Bacteria build multicellular communities termed biofilms, which are often
encased in a self-secreted extracellular matrix that gives the community
mechanical strength and protection against harsh chemicals. How bacteria
assemble distinct multicellular structures in response to different
environmental conditions remains incompletely understood. Here, we investigated
the connection between bacteria colony mechanics and the colony growth
substrate by measuring the oscillatory shear and compressive rheology of
bacteria colonies grown on agar substrates. We found that bacteria colonies
modify their own mechanical properties in response to shear and uniaxial
compression with the increasing agar concentration of their growth substrate.
These findings highlight that mechanical interactions between bacteria and
their microenvironment are an important element in bacteria colony development,
which can aid in developing strategies to disrupt or reduce biofilm growth.Comment: biophysics, soft matter, biofilm rheology, biofilm mechanic
First sequence-confirmed case of infection with the new influenza A(H1N1) strain in Germany
Here, we report on the first sequence-confirmed case of infection with the new influenza A(H1N1) virus in Germany. Two direct contacts of the patient were laboratory-confirmed as cases and demonstrate a chain of direct human-to-human transmission
Efficacy and tolerability of oral propafenone versus quinidine in the treatment of recent onset atrial fibrillation: A randomized, prospective study
Background: A prospective, randomized study was conducted to evaluate the efficacy and
tolerability of oral propafenone and quinidine for the conversion of paroxysmal atrial fibrillation
(AF).
Methods: Eighty one consecutive patients (female/male 46/35; mean age 64.0 ± 11.6),
admitted to hospital with AF lasting no longer than 48 hours, were randomized in terms of
their pharmacological therapy. Forty three patients (55%) were randomly assigned to Group I
and received propafenone 600 mg orally as the initial therapy, with an additional dose of 300 mg
after eight hours, if the sinus rhythm had not been restored by then. Thirty eight patients (45%)
(Group II) received 1 mg digoxin IV followed by an oral loading of quinidine (400 mg followed
by 200 mg every two hours).
Results: The conversion rate assessed after 24 hours was the same in both groups (Gr. I vs.
Gr. II: 90.7 vs. 91.4%), with the same number of mild side effects (Gr. I vs. Gr. II: 37.2% vs.
45.7%). No life-threatening adverse events were reported. Propafenone achieved a higher
efficacy rate during the first eight hours (83.3 vs. 54.3%; p = 0.01), with a significantly
shorter time required to sinus rhythm recovery throughout the study period, with a median
time of 165 min (95% confidence interval 120-278) vs. 360 min (95% confidence inerval
298-650; p < 0.05). There was some indication of greater effectiveness of propafenone than
quinidine in early sinus rhythm restoration in patients with: no structural heart disease, in
those with an AF duration shorter than 12 hours, and in patients with an ejection fraction > 55%.
Conclusions: Although both drugs revealed the same effectiveness, the conversion to sinus
rhythm in the group treated with propafenone was observed more quickly despite the longer
paroxysmal AF episode duration
Compressive Sensing of Signals Generated in Plastic Scintillators in a Novel J-PET Instrument
The J-PET scanner, which allows for single bed imaging of the whole human
body, is currently under development at the Jagiellonian University. The dis-
cussed detector offers improvement of the Time of Flight (TOF) resolution due
to the use of fast plastic scintillators and dedicated electronics allowing for
sam- pling in the voltage domain of signals with durations of few nanoseconds.
In this paper we show that recovery of the whole signal, based on only a few
samples, is possible. In order to do that, we incorporate the training signals
into the Tikhonov regularization framework and we perform the Principal
Component Analysis decomposition, which is well known for its compaction
properties. The method yields a simple closed form analytical solution that
does not require iter- ative processing. Moreover, from the Bayes theory the
properties of regularized solution, especially its covariance matrix, may be
easily derived. This is the key to introduce and prove the formula for
calculations of the signal recovery error. In this paper we show that an
average recovery error is approximately inversely proportional to the number of
acquired samples
System Response Kernel Calculation for List-mode Reconstruction in Strip PET Detector
Reconstruction of the image in Positron Emission Tomographs (PET) requires
the knowledge of the system response kernel which describes the contribution of
each pixel (voxel) to each tube of response (TOR). This is especially important
in list-mode reconstruction systems, where an efficient analytical
approximation of such function is required. In this contribution, we present a
derivation of the system response kernel for a novel 2D strip PET.Comment: 10 pages, 2 figures; Presented at Symposium on applied nuclear
physics and innovative technologies, Cracow, 03-06 June 201
Studies of unicellular micro-organisms Saccharomyces cerevisiae by means of Positron Annihilation Lifetime Spectroscopy
Results of Positron Annihilation Lifetime Spectroscopy (PALS) and microscopic
studies on simple microorganisms: brewing yeasts are presented. Lifetime of
ortho - positronium (o-Ps) were found to change from 2.4 to 2.9 ns (longer
lived component) for lyophilised and aqueous yeasts, respectively. Also
hygroscopicity of yeasts in time was examined, allowing to check how water -
the main component of the cell - affects PALS parameters, thus lifetime of o-Ps
were found to change from 1.2 to 1.4 ns (shorter lived component) for the dried
yeasts. The time sufficient to hydrate the cells was found below 10 hours. In
the presence of liquid water an indication of reorganization of yeast in the
molecular scale was observed.
Microscopic images of the lyophilised, dried and wet yeasts with best
possible resolution were obtained using Inverted Microscopy (IM) and
Environmental Scanning Electron Microscopy (ESEM) methods. As a result visible
changes to the surface of the cell membrane were observed in ESEM images.Comment: Nukleonika (2015
A pilot study of the novel J-PET plastic scintillator with 2-(4-styrylphenyl)benzoxazole as a wavelength shifter
For the first time a molecule of 2-(4-styrylphenyl)benzoxazole containing
benzoxazole and stilbene groups is applied as a scintillator dopant acting as a
wavelength shifter. In this article a light yield of the plastic scintillator,
prepared from styrene doped with 2 wt% of 2,5-diphenylbenzoxazole and 0.03 wt%
of 2-(4-styrylphenyl)benzoxazole, is determined to be as large as 60% 2%
of the anthracene light output. There is a potential to improve this value in
the future by the optimization of the additives concentrations
A novel method for calibration and monitoring of time synchronization of TOF-PET scanners by means of cosmic rays
All of the present methods for calibration and monitoring of TOF-PET scanner
detectors utilize radioactive isotopes such as e.g. Na or Ge,
which are placed or rotate inside the scanner. In this article we describe a
novel method based on the cosmic rays application to the PET calibration and
monitoring methods. The concept allows to overcome many of the drawbacks of the
present methods and it is well suited for newly developed TOF-PET scanners with
a large longitudinal field of view. The method enables also monitoring of the
quality of the scintillator materials and in general allows for the continuous
quality assurance of the PET detector performance.Comment: 10 pages, 7 figure
Application of the Compress Sensing Theory for Improvement of the TOF Resolution in a Novel J-PET Instrument
Nowadays, in Positron Emission Tomography (PET) systems, a Time of Flight
information is used to improve the image reconstruction process. In Time of
Flight PET (TOF-PET), fast detectors are able to measure the difference in the
arrival time of the two gamma rays, with the precision enabling to shorten
significantly a range along the line-of-response (LOR) where the annihilation
occurred. In the new concept, called J-PET scanner, gamma rays are detected in
plastic scintillators. In a single strip of J-PET system, time values are
obtained by probing signals in the amplitude domain. Owing to Compress Sensing
theory, information about the shape and amplitude of the signals is recovered.
In this paper we demonstrate that based on the acquired signals parameters, a
better signal normalization may be provided in order to improve the TOF
resolution. The procedure was tested using large sample of data registered by a
dedicated detection setup enabling sampling of signals with 50 ps intervals.
Experimental setup provided irradiation of a chosen position in the plastic
scintillator strip with annihilation gamma quanta
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