bluuebunny/crossref_metadata_2025_split huggingface dataset:
Advanced Modeling for Miniaturized Potted Smart Munitions Development
Authors: Chao Nien-Hua , DeAngelis Mario E. , Lee Jyeching , Kleinbach K. S. , Cheng Ron-Bin 
Published: February 2014

Miniaturized electronics and components are becoming more common in precision-guided artillery-launched munitions and missiles. Due to the highly dynamic nature of projectile launch, and the demands for increased structural robustness, many miniaturized smart munitions resort to a potted design in order to achieve functionality and reliability requirements. In most of these applications, the potted electronics are inactive for most of their lifetime and may be stored without environmental (temperature and humidity) controls for up to 20 years. The uncontrolled environment for smart munitions however makes the thermal management task especially difficult due to the coefficient of thermal expansion (CTE) mismatch between the potting material and the electronic components.
It has been previously observed that modeling a potted device, in support of its development through finite-element simulations, is a complex task due to the numerical-convergence issues, material properties and meshes, during simulations as well as resource limitations. In this paper, we will present a modeling/simulation methodology which can be used in the development of miniaturized potted smart munitions and the product qualification process. There are two basic tests that a potential new munition needs to satisfy: 1) a highly accelerated temperature-cycling life test (HALT), to emulate the un-controlled projectile storage environment and, 2) the extremely high-G acceleration during a projectile launch. In this paper, we will present, 1) the use of finite-element analysis to support design decisions to overcome the CTE differences between electronic components on the circuit board assembly and the potting material and, 2) the use of finite-element simulations to study and improve the survivability of the electronic components on the circuit board assembly during extremely high-G acceleration projectile launches.
A Smooth Contact Algorithm Using Cubic Spline Surface Interpolation for Rigid and Flexible Bodies
Authors: Choi Juhwan , Choi Jin Hwan 
Published: February 2014

The contact analysis of multi-flexible-body dynamics (MFBD) has been an important issue in the area of computational dynamics because the realistic dynamic analysis of many mechanical systems includes the contacts among rigid and flexible bodies. But, until now, the contact analysis in the multi-flexible-body dynamics has still remained as a big, challenging area. Especially, the most of contact algorithms have been developed based on the facetted triangles. As a result, the contact force based on the facetted surface was not accurate and smooth because the geometrical error is already included in the contact surface representation stage. This kind of error can be very important in the precise mechanism such as gear contact or cam-valve contact problems. In order to resolve this problem, this study suggests a cubic spline surface representation method and related contact algorithms.
The proposed contact algorithms are using the compliant contact force model based on the Hertzian contact theory. In order to evaluate the smooth contact force, the penetration depth and contact normal directions are evaluated by using the cubic spline surface interpolation. Also, for the robust and efficient contact algorithm development, the contact algorithms are divided into four main parts which are a surface representation, a pre-search, a detailed search and a contact force generation. In the surface representation part, we propose a smooth surface representation method which can be used for smooth rigid and flexible bodies. In the pre-search, the algorithm performs collision detection and composes the expected contact pairs for the detailed search. In the detailed search, the penetration depth and contact reference frame are calculated with the cubic spline surface interpolation in order to generate the accurate and smooth contact force. Finally in the contact force generation part, we evaluate the contact force and Jacobian matrix for the implicit time integrator.
Stakeholder and Constraint-Driven Innovation of a Novel, Lever-Propelled, All-Terrain Wheelchair
Authors: Winter Amos G. 
Published: February 2014

The Leveraged Freedom Chair (LFC) is a low-cost, all-terrain, lever-propelled wheelchair designed primarily for use in developing countries. LFC technology was conceived because 70 percent of wheelchair users in these markets live in rural areas and no currently available mobility aid enables them to travel long distances on rough terrain and maneuver in tight, indoor confines. Because developing world markets impose constraints on cost, durability, and performance, a novel solution was required to satisfy stakeholder requirements. The key innovation behind the LFC is its single speed, variable mechanical advantage lever drivetrain. The user effectively changes gear by shifting his hands along the levers; grasping near the ends increases torque, while grasping near the pivots enables a larger angular displacement with every stroke, which increases speed. The drivetrain is made from low-cost bicycle parts found throughout the developing world, which enables the LFC to be sold for $200 and be repairable anywhere.
During three user trials in East Africa, Guatemala, and India, stakeholder feedback was used to refine the chair between trials, resulting in a device 9.1 kg (20 lbs) lighter, 8.9 cm (3.5 in) narrower, and with a center of gravity 12.7 cm (5 in) lower than the first iteration. Survey data substantiated increases in performance after successive iterations. Quantitative biomechanical performance data were also measured during the Guatemala and India trials, which showed the LFC to be 76 percent faster and 41 percent more efficient during a common daily commute, and able to produce 53 percent higher peak propulsion force compared to conventional, pushrim-propelled wheelchairs. The LFC offers comparable performance at less than one-twentieth the cost of off road wheelchairs available in the rich world. Stakeholder feedback and the highly-constrained environment for which the LFC was created drove the technology towards a novel, innovative solution that offers a competitive advantage in both developing and developed markets. The paper concludes with a description of how the LFC is a “constraint-driven innovation.” This idea ties together the theories of “disruptive innovation” and “reverse innovation,” and may be used as a design tool for engineers striving to create technologies that have global impact.
Analysis of Polymer Micro Fibers: A Smoothed Particle Hydrodynamics Approach
Authors: Cramer Nick , Teodorescu M. 
Published: February 2014

The nanofibrillar array of a Gecko inspired Synthetic Adhesive (GSA) adheres to a surfaces when fibers undergo deformations of both the stems and the tip. The GSA’s show interesting changes in effectiveness dependent on use patterns, preloads, and material types, amongst other parameters. The polymers fibers also, display plastic creep even at relatively low strain rates and stresses below plastic yield. Therefore, a suitable numerical solution, which predicts the fiber geometry, must consider not only the initial shape of the fiber, but also the fiber progressive deformation (local and global) and the influence this has on the local mechanical properties (elastic, viscoelastic, strain hardening/softening and plastic flow). The localized mechanical properties are difficult to calculate using traditional methods because of the nonlinearities associated with viscoelastic effects, the large deformations, and the variable boundary conditions. However, the variable boundary conditions make a mesh free modeling method ideal. Smooth Particle Hydrodynamics (SPH) is one of the most prominent mesh free Lagrange method, which takes a set particle and uses particle kinematics, density gradients, and material properties to determine the interaction between particles.
As a first step towards modeling the behavior of a fibrillar adhesive surface, this paper focuses on the modeling of a single polymer fiber. The single micro fiber will be subjected to similar conditions to what it would see as part of an array. This will allow the SPH method of simulation to be critiqued for its further use in simulating polymer microfiber. While the localized mechanical properties of the polymer, which depend on viscoelastic effect and other nonlinear phenomena, are difficult to determine analytically. The modeling technique can be compared to standard analytical methods for global parameters. It was found that the SPH method was able to appropriately model the effect of various scenarios on the mechanical deformation and resonance of a polymer microfiber. Further more the friction force for the fiber on glass was calculated as were the localized fiber velocities and stresses.
A Method for Multiaxial Fatigue Reliability Analysis Based on Mixed Weibull Distribution
Authors: Ling Dan , Huang Hong-Zhong , Wang Song , Wu Chuan-hao , Zhu Shun-peng , Zhang Xiao-Ling 
Published: February 2014

The fatigue life of mechanical element is a random variable in nature following some kind of statistical distribution.
In this paper, a method for reliability life prediction considering life randomness is proposed. Firstly, the Smith-Watson-Topper (SWT) model is used to describe the relationship of the maximum normal stress and strain range on the critical plane. Secondly, the maximum normal stress and strain range on the critical plane are calculated by finite element analysis. Thirdly, fatigue life samples are generated using Monte Carlo simulation method, and the mixed Weibull distribution is used to model the distribution of fatigue life of turbine discs. Finally, the proposed method is validated by comparing the prediction results from the proposed method, the observed cumulative failure probability based on median rank, and the standard two-parameter Weibull distribution.
Observations Regarding Numerical Results Obtained by the Floquet-Method
Authors: Kniffka Till J. , Ecker Horst 
Published: February 2014

Stability studies of parametrically excited systems are frequently carried out by numerical methods. Especially for LTP-systems, several such methods are known and in practical use. This study investigates and compares two methods that are both based on Floquet’s theorem.
As an introductary benchmark problem a 1-dof system is employed, which is basically a mechanical representation of the damped Mathieu-equation. The second problem to be studied in this contribution is a time-periodic 2-dof vibrational system. The system equations are transformed into a modal representation to facilitate the application and interpretation of the results obtained by different methods.
Both numerical methods are similar in the sense that a monodromy matrix for the LTP-system is calculated numerically. However, one method uses the period of the parametric excitation as the interval for establishing that matrix. The other method is based on the period of the solution, which is not known exactly.
Numerical results are computed by both methods and compared in order to work out how they can be applied efficiently.
In Vitro
and
In Vivo
Activities of Pterostilbene against Candida albicans Biofilms
Authors: Li De-Dong , Zhao Lan-Xue , Mylonakis Eleftherios , Hu Gan-Hai , Zou Yong , Huang Tong-Kun , Yan Lan , Wang Yan , Jiang Yuan-Ying 
Published: February 2014

ABSTRACT

Pterostilbene (PTE) is a stilbene-derived phytoalexin that originates from several natural plant sources. In this study, we evaluated the activity of PTE against
Candida albicans
biofilms and explored the underlying mechanisms. In 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) reduction assays, biofilm biomass measurement, confocal laser scanning microscopy, and scanning electron microscopy, we found that ≤16 μg/ml PTE had a significant effect against
C. albicans
biofilms
in vitro
, while it had no fungicidal effect on planktonic
C. albicans
cells, which suggested a unique antibiofilm effect of PTE. Then we found that PTE could inhibit biofilm formation and destroy the maintenance of mature biofilms. At 4 μg/ml, PTE decreased cellular surface hydrophobicity (CSH) and suppressed hyphal formation. Gene expression microarrays and real-time reverse transcription-PCR showed that exposure of
C. albicans
to 16 μg/ml PTE altered the expression of genes that function in morphological transition, ergosterol biosynthesis, oxidoreductase activity, and cell surface and protein unfolding processes (heat shock proteins). Filamentation-related genes, especially those regulated by the Ras/cyclic AMP (cAMP) pathway, including
ECE1
,
ALS3
,
HWP1
,
HGC1
, and
RAS1
itself, were downregulated upon PTE treatment, indicating that the antibiofilm effect of PTE was related to the Ras/cAMP pathway. Then, we found that the addition of exogenous cAMP reverted the PTE-induced filamentous growth defect. Finally, with a rat central venous catheter infection model, we confirmed the
in vivo
activity of PTE against
C. albicans
biofilms. Collectively, PTE had strong activities against
C. albicans
biofilms both
in vitro
and
in vivo
, and these activities were associated with the Ras/cAMP pathway.
Synthesis and Antifungal Activity
In Vitro
of Isoniazid Derivatives against Histoplasma capsulatum var. capsulatum
Authors: de Aguiar Cordeiro Rossana , de Farias Marques Francisca Jakelyne , de Aguiar Cordeiro Rebecca , da Silva Marcos Reinaldo , Donato Maia Malaquias Angela , Silva de Melo Charlline Vládia , Mafezoli Jair , Ferreira de Oliveira Maria da Conceição , Nogueira Brilhante Raimunda Sâmia , Gadelha Rocha Marcos Fábio , Pinheiro Gomes Bandeira Tereza de Jesus , Costa Sidrim José Júlio 
Published: February 2014

ABSTRACT

Histoplasmosis is a severe infection that affects millions of patients worldwide and is endemic in the Americas. Amphotericin B (AMB) and itraconazole are highly effective for the treatment of severe and milder forms of the disease, but AMB is toxic, and the bioavailability of itraconazole is erratic. Therefore, it is important to investigate new classes of drugs for histoplasmosis treatment. In this study, a series of nine isoniazid hydrazone derivatives were synthesized and evaluated for their antifungal activities
in vitro
against the dimorphic fungus
Histoplasma capsulatum
var.
capsulatum
. The drugs were tested by microdilution in accordance with CLSI guidelines. The compound
N
′-(1-phenylethylidene)isonicotinohydrazide had the lowest MIC range of all the compounds for the yeast and filamentous forms of
H. capsulatum
. The
in vitro
synergy of this compound with AMB against the planktonic and biofilm forms of
H. capsulatum
cells was assessed by the checkerboard method. The effects of this hydrazone on cellular ergosterol content and membrane integrity were also investigated. The study showed that the compound alone is able to reduce the ergosterol content of planktonic cells and can alter the membrane permeability of the fungus. Furthermore, the compound alone or in combination with AMB showed inhibitory effects against mature biofilms of
H. capsulatum
.
N
′-(1-Phenylethylidene)isonicotinohydrazide alone or combined with AMB might be of interest in the management of histoplasmosis.
Comparative Study of Genotype and Virulence in CTX-M-Producing and Non-Extended-Spectrum-β-Lactamase-Producing Klebsiella pneumoniae Isolates
Authors: Shin Juyoun , Ko Kwan Soo 
Published: February 2014

ABSTRACT

Molecular and virulence characteristics of CTX-M-producing and non-extended-spectrum-β-lactamase (non-ESBL)-producing
Klebsiella pneumoniae
isolates were compared. Lack of shared characteristics between the two groups suggested that most CTX-M-producing
K. pneumoniae
isolates in South Korea did not occur by transfer of
bla
CTX-M
into susceptible strains. Conjugation assays confirmed that the plasmid with the
bla
CTX-M-15
gene confers virulence as well as antimicrobial resistance, suggesting that a CTX-M-15-producing clone such as ST11 may have a selective advantage even without antibiotic pressure.
Moxifloxacin Retains Antimycobacterial Activity in the Presence of
gyrA
Mutations
Authors: McGrath Marieta , Gey van Pittius Nico C. , Sirgel Frederick A. , Van Helden Paul D. , Warren Robin M. 
Published: February 2014

ABSTRACT

Moxifloxacin-resistant
Mycobacterium tuberculosis
mutants were selected
in vitro
using different concentrations of moxifloxacin.
gyrA
mutations at codons 88 and 94 were associated with resistance (defined as an MIC of ≥2 μg/ml) (
P
< 0.0001 and
P
= 0.0053, respectively). Despite the presence of
gyrA
mutations, moxifloxacin significantly impedes bacterial growth, supporting its use for the treatment of ofloxacin-resistant
M. tuberculosis
.
Temporins A and B Stimulate Migration of HaCaT Keratinocytes and Kill Intracellular Staphylococcus aureus
Authors: Di Grazia Antonio , Luca Vincenzo , Segev-Zarko Li-av T. , Shai Yechiel , Mangoni Maria Luisa 
Published: February 2014

ABSTRACT

The growing number of microbial pathogens resistant to available antibiotics is a serious threat to human life. Among them is the bacterium
Staphylococcus aureus
, which colonizes keratinocytes, the most abundant cell type in the epidermis. Its intracellular accumulation complicates treatments against resulting infections, mainly due to the limited diffusion of conventional drugs into the cells. Temporins A (Ta) and B (Tb) are short frog skin antimicrobial peptides (AMPs). Despite extensive studies regarding their antimicrobial activity, very little is known about their activity on infected cells or involvement in various immunomodulatory functions. Here we show that Tb kills both ATCC-derived and multidrug-resistant clinical isolates of
S. aureus
within infected HaCaT keratinocytes (80% and 40% bacterial mortality, respectively) at a nontoxic concentration, i.e., 16 μM, whereas a weaker effect is displayed by Ta. Furthermore, the peptides prevent killing of keratinocytes by the invading bacteria. Further studies revealed that both temporins promote wound healing in a monolayer of HaCaT cells, with front speed migrations of 19 μm/h and 12 μm/h for Ta and Tb, respectively. Migration is inhibited by mitomycin C and involves the epidermal growth factor receptor (EGFR) signaling pathway. Finally, confocal fluorescence microscopy indicated that the peptides diffuse into the cells. By combining antibacterial and wound-healing activities, Ta and Tb may act as multifunctional mediators of innate immunity in humans. Particularly, their nonendogenous origin may reduce microbial resistance to them as well as the risk of autoimmune diseases in mammals.
Respiratory Microbiota Dynamics following Streptococcus pneumoniae Acquisition in Young and Elderly Mice
Authors: Krone Cassandra L. , Biesbroek Giske , Trzciński Krzysztof , Sanders Elisabeth A. M. , Bogaert Debby 
Published: February 2014

ABSTRACT

The upper respiratory tract (URT) is a distinct microbial niche of low-density bacterial communities and, also, a portal of entry for many potential pathogens, including
Streptococcus pneumoniae
. Thus far, animal models have been used to study the dynamics of and interactions between limited numbers of different species in the URT. Here, we applied a deep sequencing approach to explore, for the first time, the impact of
S. pneumoniae
acquisition on URT microbiota in a mouse model, as well as potential age-dependent effects. Young-adult and elderly mice were inoculated intranasally with
S. pneumoniae
, and nasal lavage samples were collected for up to 28 days postcolonization. Bacterial DNA extracted from lavage samples was subjected to barcoded pyrosequencing of the V5-to-V7 hypervariable region of the small-subunit rRNA gene. We observed highly diverse microbial profiles, with the presence overall of 15 phyla and approximately 645 operational taxonomic units (OTUs). We noted differences in the composition of microbiota between young and elderly mice, with a significantly higher abundance of
Bacteroidetes
in the young mice. The introduction of
S. pneumoniae
into the URT led to a temporary dominance of pneumococci in the microbiota of all mice, accompanied by a significant decrease in microbial diversity. As mice gradually cleared the colonization, the diversity returned to baseline levels. Diversification was accompanied by an early expansion of
Bacteroidetes
,
Staphylococcus
spp., and
Lachnospiraceae
. Moreover, the
Bacteroidetes
expansion was significantly greater in young-adult than in elderly mice. In conclusion, we observed differences in URT microbiota composition between naive young-adult and elderly mice that were associated with differences in pneumococcal clearance over time.
Natural Disruption of Two Regulatory Networks in Serotype M3 Group A Streptococcus Isolates Contributes to the Virulence Factor Profile of This Hypervirulent Serotype
Authors: Cao Tram N. , Liu Zhuyun , Cao Tran H. , Pflughoeft Kathryn J. , Treviño Jeanette , Danger Jessica L. , Beres Stephen B. , Musser James M. , Sumby Paul 
Published: February 2014

ABSTRACT

Despite the public health challenges associated with the emergence of new pathogenic bacterial strains and/or serotypes, there is a dearth of information regarding the molecular mechanisms that drive this variation. Here, we began to address the mechanisms behind serotype-specific variation between serotype M1 and M3 strains of the human pathogen
Streptococcus pyogenes
(the group A
Streptococcus
[GAS]). Spatially diverse contemporary clinical serotype M3 isolates were discovered to contain identical inactivating mutations within genes encoding two regulatory systems that control the expression of important virulence factors, including the thrombolytic agent streptokinase, the protease inhibitor-binding protein-G-related α
2
-macroglobulin-binding (GRAB) protein, and the antiphagocytic hyaluronic acid capsule. Subsequent analysis of a larger collection of isolates determined that M3 GAS, since at least the 1920s, has harbored a 4-bp deletion in the
fasC
gene of the
fasBCAX
regulatory system and an inactivating polymorphism in the
rivR
regulator-encoding gene. The
fasC
and
rivR
mutations in M3 isolates directly affect the virulence factor profile of M3 GAS, as evident by a reduction in streptokinase expression and an enhancement of GRAB expression. Complementation of the
fasC
mutation in M3 GAS significantly enhanced levels of the small regulatory RNA FasX, which in turn enhanced streptokinase expression. Complementation of the
rivR
mutation in M3 GAS restored the regulation of
grab
mRNA abundance but did not alter capsule mRNA levels. While important, the
fasC
and
rivR
mutations do not provide a full explanation for why serotype M3 strains are associated with unusually severe invasive infections; thus, further investigation is warranted.