410 research outputs found
Open Photoacoustic Cell for Blood Sugar Measurement: Numerical Calculation of Frequency Response
A new approach for continuous and non-invasive monitoring of the glucose
concentration in human epidermis has been suggested recently. This method is
based on photoacoustic (PA) analysis of human interstitial fluid. The
measurement can be performed in vitro and in vivo and, therefore, may form the
basis for a non-invasive monitoring of the blood sugar level for diabetes
patients. It requires a windowless PA cell with an additional opening that is
pressed onto the human skin. Since signals are weak, advantage is taken of
acoustic resonances of the cell. Recently, a numerical approach based on the
Finite Element (FE) Method has been successfully used for the calculation of
the frequency response function of closed PA cells. This method has now been
adapted to obtain the frequency response of the open cell. Despite the fact
that loss due to sound radiation at the opening is not included, fairly good
accordance with measurement is achieved
Photoacoustics Modelling using Amplitude Mode Expansion Method in a Multiscale T-cell Resonator
The photoacoustic (PA) effect consisting of the generation of an acoustic
signal based on the absorption of light has already demonstrated its potential
for various spectroscopic applications for both gaseous and solid samples. The
signal produced during photoacoustic spectroscopy (PAS) measurement is,
however, usually weak and needs to be amplified. This is achieved by using a
photoacoustic cell resonator where acoustic resonances are utilized to
significantly boost the signal. Therefore, a PA resonator has a significant
role in PAS measurement set-ups. When designing or optimizing a new PA
resonator, numerical methods are generally used to simulate the photoacoustic
signal generation. In this paper, the amplitude mode expansion (AME) method is
presented as a quick and accurate simulation tool. The method is used to
simulate the photoacoustic signal in a multi-scale T-cell resonator over a wide
frequency range. The AME method is based on eigenmode expansion and
introduction of losses by quality factors. The AME simulation results are
compared and analyzed against the results from the viscothermal method.
Reasonably good agreement is obtained between the two methods. However, small
frequency shifts in the resonances of the AME method are noted. The shifts are
attributed to the location of the dominant mode within the T-cell. The
viscothermal method is considered the most accurate method for simulating the
photoacoustic signal in small resonators. However, it is computationally very
demanding. The AME method provides a much faster simulation alternative. This
is particularly useful in the design and optimization of photoacoustic
resonators where numerical methods are preferred over experimental measurements
due to their speed and low cost.Comment: Comsol Conference 201
Backcoupling of acoustic streaming on the temperature field inside high-intensity discharge lamps
Operating high-intensity discharge lamps in the high frequency range (20-300
kHz) provides energy-saving and cost reduction potentials. However,
commercially available lamp drivers do not make use of this operating strategy
because light intensity fluctuations and even lamp destruction are possible.
The reason for the fluctuating discharge arc are acoustic resonances in this
frequency range that are excited in the arc tube. The acoustic resonances in
turn generate a fluid flow that is caused by the acoustic streaming effect.
Here, we present a 3D multiphysics model to determine the influence of acoustic
streaming on the temperature field in the vicinity of an acoustic
eigenfrequency. In that case a transition from stable to instable behavior
occurs. The model is able to predict when light flicker can be expected. The
results are in very good accordance with accompanying experiments
High-Intensity Discharge Lamp and Duffing Oscillator - Similarities and Differences
The processes inside the arc tube of high-intensity discharge lamps are
investigated by finite element simulations. The behavior of the gas mixture
inside the arc tube is governed by differential equations describing mass,
energy and charge conservation as well as the Helmholtz equation for the
acoustic pressure and the Navier-Stokes equation for the flow driven by the
buoyancy and the acoustic streaming force. The model is highly nonlinear and
requires a recursion procedure to account for the impact of acoustic streaming
on the temperature and other fields. The investigations reveal the presence of
a hysteresis and the corresponding jump phenomenon, quite similar to a Duffing
oscillator. The similarities and, in particular, the differences of the
nonlinear behavior of the high-intensity discharge lamp to that of a Duffing
oscillator are discussed. For large amplitudes the high-intensity discharge
lamp exhibits a stiffening effect in contrast to the Duffing oscillator.Comment: 14 pages, 8 figure
Neue Funde von Lepthyphantes geniculatus in Sachsen-Anhalt (Araneae, Linyphiidae)
Vorkommen desselten gefundenen Lepthyphantes geniculatus KULCZYNSKI, 1898 sind aus Deutschland bisher nur vom Gipskarstgebiet des Kyffhäusers (N-Thüringen) bekannt. 1964 und 1965 wurden dort auf zwei Gipshügeln in der Umgebung von Bad Frankenhausen insgesamt 4 männliche und 2 weibliche in Bodenfallen nachgewiesen (v. BROEN 1965, 1966)
Determining the most suitable spectral range for TDLS – a quantitative approach
We present a mathematical method which allows determination of an optimal spectral range for gas mixture analysis based on theoretical absorption spectra. The resulting center wavelength is particularly suited for tunable diode laser spectroscopy (TDLS). The procedure contains several steps of numerical calculations which can easily be implemented in almost any programming language. We apply our method to three exemplary mixtures of hydrocarbons and present and validate the individual results.Hochschule für Angewandte Wissenschaften HamburgBundesministerium für Umwelt, Naturschutz, Nukleare Sicherheit und VerbraucherschutzPeerReviewe
On the Necessity for High-availability Data Center Backends in a Distributed Wireless System
When business processes depend on the processing capabilities within a data center, the typical system architecture use a high-availability setup to maintain a high level of service. Faced with a specific machine-to-machine system consisting of many endpoints that collect and forward data to the data center we argue that the dependability of the overall system does not necessitate a high level of service for the data center components. Taking an existing discrete event simulation model of a distributed technical system we investigate and discuss the effects of prolonged outages of the data center on the major business processes of the system
Distribution of serotonergic and dopaminergic nerve fibers in the salivary gland complex of the cockroach Periplaneta americana
BACKGROUND: The cockroach salivary gland consists of secretory acini with peripheral ion-transporting cells and central protein-producing cells, an extensive duct system, and a pair of reservoirs. Salivation is controled by serotonergic and dopaminergic innervation. Serotonin stimulates the secretion of a protein-rich saliva, dopamine causes the production of a saliva without proteins. These findings suggest a model in which serotonin acts on the central cells and possibly other cell types, and dopamine acts selectively on the ion-transporting cells. To examine this model, we have analyzed the spatial relationship of dopaminergic and serotonergic nerve fibers to the various cell types. RESULTS: The acinar tissue is entangled in a meshwork of serotonergic and dopaminergic varicose fibers. Dopaminergic fibers reside only at the surface of the acini next to the peripheral cells. Serotonergic fibers invade the acini and form a dense network between central cells. Salivary duct segments close to the acini are locally associated with dopaminergic and serotonergic fibers, whereas duct segments further downstream have only dopaminergic fibers on their surface and within the epithelium. In addition, the reservoirs have both a dopaminergic and a serotonergic innervation. CONCLUSION: Our results suggest that dopamine is released on the acinar surface, close to peripheral cells, and along the entire duct system. Serotonin is probably released close to peripheral and central cells, and at initial segments of the duct system. Moreover, the presence of serotonergic and dopaminergic fiber terminals on the reservoir indicates that the functions of this structure are also regulated by dopamine and serotonin
Homozygosity mapping reveals new nonsense mutation in the FAM161A gene causing autosomal recessive retinitis pigmentosa in a Palestinian family
Purpose: Retinitis pigmentosa (RP) is a heterogenous group of inherited retinal degenerations caused by mutations in at least 45 genes. Recently, the FAM161A gene was identified as the causative gene for RP28, an autosomal recessive form of RP.
Methods: We performed a clinical and molecular genetic study of a consanguineous Palestinian family with two three siblings affected with retinitis pigmentosa. DNA samples were collected from the index patient, his father, his affected sister, and two non-affected brothers. DNA sample from the index was subjected to high resolution genome-wide SNP array. Assuming identity-by-descent in this consanguineous family we applied homozygosity mapping to identify disease causing genes.
Results: The index patient reported night blindness since the age of 20 years, followed by moderate disease progression with decrease of peripheral vision, the development of photophobia and later on reduced central vision. At the age of 40 his visual acuity was counting fingers (CF) for both eyes, color discrimination was not possible and his visual fields were severely constricted. Funduscopic examination revealed a typical appearance of advanced RP with optic disc pallor, narrowed retinal vessels, bone-spicule like pigmentary changes in the mid-periphery and atrophic changes in the macula. His younger affected brother (37 years) was reported with overall milder symptoms, while the youngest sister (21 years) reported problems only with night vision. Applying high-density SNP arrays we identified several homozygous genomic regions one of which included the recently identified FAM161A gene mutated in RP28-linked autosomal recessive RP. Sequencing analysis revealed the presence of a novel homozygous nonsense mutation, c.1003C>T/p.R335X in the index patient and the affected sister.
Conclusion: We identified an RP28-linked RP family in the Palestinian population caused by a novel nonsense mutation in FAM161A. RP in this family shows a typical disease onset with moderate to rapid progression into severe visual impairment including central vision in the index and overall milder symptoms in the younger brother and sister.We thank the family members for participation in this study. We also thank the Microarray Facility at the Medical Faculty of the Tübingen University for SNP chip processing. This work was supported by a Trilateral German-Israel-Palestinian Authority program grant of the Deutsche Forschungsgemeinschaft (SCHO 754/5–1 and WI1189/8–1)
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