10,791 research outputs found
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A Parametric Study of Part Distortions in FDM Using 3D FEA
We developed a finite element model to simulate the fused deposition modeling (FDM)
process. The model considers the coupled thermal and mechanical analysis and incorporates the
element activation function to mimic the additive nature of FDM. Due to repetitive heating and
cooling in the FDM process, residual stresses accumulate inside the part during the deposition.
The model is also used to evaluate the part distortions, revealing distortion features such as
vaulting shapes and distortion-core shifting. A parametric study, three factors and three levels,
was performed to evaluate the effects of the deposition parameters on residual stresses and part
distortions. Prototype models with larger sizes were fabricated, measured, and compared with the
simulations.
The simulation results show that (1) the scan speed is the most significant factor to part
distortions, followed by the layer thickness, (2) the road width alone is insignificant, however,
the interaction between the road width and the layer thickness is significant too, and (3) there are
other two-way and three-way interactions that are of secondary significance. Residual stresses
increase with the layer thickness, and increase with the road width, to a less extent though, yet
largely affected by the layer thickness. The FDM part distortions from the experiment show a
similar trend as in the simulations, but no quantitative correlation.Mechanical Engineerin
Anonymity and Information Hiding in Multiagent Systems
We provide a framework for reasoning about information-hiding requirements in
multiagent systems and for reasoning about anonymity in particular. Our
framework employs the modal logic of knowledge within the context of the runs
and systems framework, much in the spirit of our earlier work on secrecy
[Halpern and O'Neill 2002]. We give several definitions of anonymity with
respect to agents, actions, and observers in multiagent systems, and we relate
our definitions of anonymity to other definitions of information hiding, such
as secrecy. We also give probabilistic definitions of anonymity that are able
to quantify an observer s uncertainty about the state of the system. Finally,
we relate our definitions of anonymity to other formalizations of anonymity and
information hiding, including definitions of anonymity in the process algebra
CSP and definitions of information hiding using function views.Comment: Replacement. 36 pages. Full version of CSFW '03 paper, submitted to
JCS. Made substantial changes to Section 6; added references throughou
Minimal Permutations and 2-Regular Skew Tableaux
Bouvel and Pergola introduced the notion of minimal permutations in the study
of the whole genome duplication-random loss model for genome rearrangements.
Let denote the set of minimal permutations of length
with descents, and let . They derived that
and , where is the -th
Catalan number. Mansour and Yan proved that . In
this paper, we consider the problem of counting minimal permutations in
with a prescribed set of ascents. We show that such
structures are in one-to-one correspondence with a class of skew Young
tableaux, which we call -regular skew tableaux. Using the determinantal
formula for the number of skew Young tableaux of a given shape, we find an
explicit formula for . Furthermore, by using the Knuth equivalence,
we give a combinatorial interpretation of a formula for a refinement of the
number .Comment: 19 page
The Effects of Extending the Spectral Information Acquired by a Photon-counting Detector for Spectral CT
Photon-counting x-ray detectors with pulse-height analysis provide spectral information that may improve material decomposition and contrast-to-noise ratio (CNR) in CT images. The number of energy measurements that can be acquired simultaneously on a detector pixel is equal to the number of comparator channels. Some spectral CT designs have a limited number of comparator channels, due to the complexity of readout electronics. The spectral information could be extended by changing the comparator threshold levels over time, sub pixels, or view angle. However, acquiring more energy measurements than comparator channels increases the noise and/or dose, due to differences in noise correlations across energy measurements and decreased dose utilisation. This study experimentally quantified the effects of acquiring more energy measurements than comparator channels using a bench-top spectral CT system. An analytical and simulation study modeling an ideal detector investigated whether there was a net benefit for material decomposition or optimal energy weighting when acquiring more energy measurements than comparator channels. Experimental results demonstrated that in a two-threshold acquisition, acquiring the high-energy measurement independently from the low-energy measurement increased noise standard deviation in material-decomposition basis images by factors of 1.5–1.7 due to changes in covariance between energy measurements. CNR in energy-weighted images decreased by factors of 0.92–0.71. Noise standard deviation increased by an additional factor of due to reduced dose utilisation. The results demonstrated no benefit for two-material decomposition noise or energy-weighted CNR when acquiring more energy measurements than comparator channels. Understanding the noise penalty of acquiring more energy measurements than comparator channels is important for designing spectral detectors and for designing experiments and interpreting data from prototype systems with a limited number of comparator channels
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Chronic toxicity of inhaled thymol in lungs and respiratory tracts in mouse model.
Epinephrine HFA (Primatene® Mist) is a newly formulated asthma metered dose inhaler developed to replace the previous Primatene® Mist CFC. The formulation of Epinephrine HFA contains thymol, a substance recognized to be safe by the FDA. Although the content of thymol contained in Epinephrine HFA is much lower compared to many common foods and medications available, there are no known nonclinical data about the chronic toxicity of thymol through inhalation. Two sequential 6-month studies of identical design were conducted to assess the chronic toxicity of inhaled thymol in mice. Four treatment groups, (a) Air; (b) vehicle control; (c) Article-1 (thymol 0.1%); and (d) Article-2 (thymol 0.5%) were assessed in 128 mice for 26 weeks. The mice were sacrificed at the end of the treatment period and a histopathologic evaluation was performed with respect to lungs, bronchial lymph nodes, nasal passages/nasopharynx, and trachea. Forty-five pathologic assessment parameters (PAPs) were evaluated. In total, 5591 data points from 487 mouse organs were assessed. Chronic toxicity index was calculated for 16 PAPs that had multiple histopathologic abnormal observations. The t tests were conducted for these 16 PAPs (Articles-1 and 2 versus Air and vehicle control, respectively), and all P-values were greater than .05 indicating no significant differences between all treatment groups. An evaluation was also conducted for 25 PAPs that had only a very small number of pathologic abnormalities. No significant differences for chronic toxicity were found when comparing mice under long-term repeated exposure of high doses of inhaled thymol and mice that inhaled no thymol
Pharmacokinetic study of thymol after intravenous injection and high-dose inhalation in mouse model.
Thymol is generally recognized as a safe substance by the FDA and has been widely used in the pharmaceutical, food, and cosmetic industries. Pharmacokinetic (PK) studies of thymol have been previously conducted for oral administration, but there has been no PK study for inhalation administration or intravenous (IV) injection. This study aims at exploring and comparing the inhalation and IV PK profile of thymol in a mouse model. The inhalation PK for mouse model was corrected with fur/skin absorption. Thirty-two male CD-1 mice were randomized into two study arms, Arm-A for intravenous (n = 16) and Arm-B for inhalation (n = 16). The amount of thymol in the mouse serum was measured for Arm-A and for Arm-B at the highest dose. Furthermore, 48 mice were utilized for fur/skin absorption of thymol. In total, 320 mouse serum samples for thymol were analyzed by LC/MS method. After inhalation, the peak concentration of thymol in mouse serum was 42.3 ng/mL (Cmax ) and occurred at 2 minutes (tmax ). The AUC of the inhaled thymol at 0-60 minutes (AUC0-60) was 464 ng/mL/min. From 10-60 minutes post-dose, the PK inhalation curve appeared to be higher than that for the IV injection. This is likely attributed to the effect of absorption of thymol through the fur/skin of mice. After an adjustment by fur/skin absorption, the PK profile for net inhalation closely matched the two-compartment model. In fact, the bioavailability for the net inhalation of thymol was 74% and 77% relative to that for IV injection per AUC0-60min and AUC0-infinite, respectively
Sense of Community and Political Mobilization in Virtual Communities: The Role of Dispositional and Situational Variables
This paper explores the psychological processes that connect virtual communities to political behavior. Drawing on previous findings in political psychology, I argue that the psychological sense of community may be an important mechanism that dictates people’s behavioral responses toward incoming information or mobilization pressure in the online environment. I then discuss the role of different dispositional and situational variables in: a) contributing to the formation of sense of community in the virtual world, and b) serving as potential moderators to influence the strength of virtual sense of community and its subsequent impact on individuals’ political behavior. Finally, I consider the methodological approaches that may be used as well as the theoretical implications for future research in this area
What are the most effective treatments for bacterial vaginosis in nonpregnant women?
Either oral or vaginal metronidazole or vaginal clindamycin provides equivalent treatment for bacterial vaginosis in nonpregnant women. Oral clindamycin 300 mg twice daily for 7 days is an effective alternative. There is conflicting evidence regarding the efficacy of a single 2-g dose of oral metronidazole. Ofloxacin 200 mg or 300 mg twice daily is less effective but could be considered for women with intolerance to metronidazole or clindamycin. Overall recurrence rates of up to 30% have been reported. (Grade of recommendation: A, based on systematic reviews and randomized controlled trials
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