400 research outputs found
Nonlinear modal interactions in clamped-clamped mechanical resonators
A theoretical and experimental investigation is presented on the intermodal
coupling between the flexural vibration modes of a single clamped-clamped beam.
Nonlinear coupling allows an arbitrary flexural mode to be used as a
self-detector for the amplitude of another mode, presenting a method to measure
the energy stored in a specific resonance mode. Experimentally observed complex
nonlinear dynamics of the coupled modes are quantitatively captured by a model
which couples the modes via the beam extension; the same mechanism is
responsible for the well-known Duffing nonlinearity in clamped-clamped beams.Comment: 5 pages, 3 figure
Enzymatic post-crosslinking of printed hydrogels of methacrylated gelatin and tyramine-conjugated 8-arm poly(ethylene glycol) to prepare interpenetrating 3D network structures
Methacrylated gelatin (GelMA) has been intensively studied as a 3D printable scaffold material in tissue regeneration fields, which can be attributed to its well-known biological functions. However, the long-term stability of photo-crosslinked GelMA scaffolds is hampered by a combination of its fast degradation in the presence of collagenase and the loss of physical crosslinks at higher temperatures. To increase the longer-term shape stability of printed scaffolds, a mixture of GelMA and tyramine-conjugated 8-arm PEG (8PEGTA) was used to create filaments composed of an interpenetrating network (IPN). Photo-crosslinking during filament deposition of the GelMA and subsequent enzymatic crosslinking of the 8PEGTA were applied to the printed 3D scaffolds. Although both crosslinking mechanisms are radical based, they operate without interference of each other. Rheological data of bulk hydrogels showed that the IPN was an elastic hydrogel, having a storage modulus of 6 kPa, independent of temperature in the range of 10 â 40°C. Tensile and compression moduli were 110 kPa and 80 kPa, respectively. On enzymatic degradation in the presence of collagenase, the gelatin content of the IPN fully degraded in 7 days, leaving a stable secondary crosslinked 8PEGTA network. Using a BioMaker bioprinter, hydrogels without and with human osteosarcoma cells (hMG-63) were printed. On culturing for 21 days, hMG-63 in the GelMA/8PEGTA IPN showed a high cell viability (>90%). Thus, the presence of the photoinitiator, incubation with H2O2, and mechanical forces during printing did not hamper cell viability. This study shows that the GelMA/8PEGTA ink is a good candidate to generate cell-laden bioinks for extrusion-based printing of constructs for tissue engineering applications.</p
In Vitro and In Vivo Degradation of PhotoâCrosslinked Poly(Trimethylene CarbonateâcoâΔâCaprolactone) Networks
Three-armed poly(trimethylene carbonate) (PTMC) and poly(trimethylene carbonate-co-Æ-caprolactone) (P(TMC-co-Δ-CL)) macromers with molecular weights of approximately 30 kg molâ1 are synthesized by ring-opening polymerization and subsequent functionalization with methacrylic anhydride. Networks are then prepared by photo-crosslinking. To investigate the in vitro and in vivo degradation properties of these photo-crosslinked networks and assess the effect of Δ-caprolactone content on the degradation properties, PTMC networks, and copolymer networks with two different TMC:Δ-CL ratios are prepared. PTMC networks degraded slowly, via an enzymatic surface erosion process, both in vitro and in vivo. Networks prepared from P(TMC-co-Δ-CL) macromers with a 74:26 ratio are found to degrade slowly as well, via a surface erosion process, albeit at a higher rate compared to PTMC networks. Increasing the Δ-CL content to a ratio of 52:48, resulted in a faster degradation. These networks lost their mechanical properties much sooner than the other networks. Thus, PTMC and P(TMC-co-Δ-CL) networks are interesting networks for tissue engineering purposes and the exact degradation properties can be tuned by varying the TMC:Δ-CL ratio, providing researchers with a tool to obtain copolymer networks with the desired degradation rate depending on the intended application
Coupling carbon nanotube mechanics to a superconducting circuit
The quantum behaviour of mechanical resonators is a new and emerging field
driven by recent experiments reaching the quantum ground state. The high
frequency, small mass, and large quality-factor of carbon nanotube resonators
make them attractive for quantum nanomechanical applications. A common element
in experiments achieving the resonator ground state is a second quantum system,
such as coherent photons or superconducting device, coupled to the resonators
motion. For nanotubes, however, this is a challenge due to their small size.
Here, we couple a carbon nanoelectromechanical (NEMS) device to a
superconducting circuit. Suspended carbon nanotubes act as both superconducting
junctions and moving elements in a Superconducting Quantum Interference Device
(SQUID). We observe a strong modulation of the flux through the SQUID from
displacements of the nanotube. Incorporating this SQUID into superconducting
resonators and qubits should enable the detection and manipulation of nanotube
mechanical quantum states at the single-phonon level
Eye Size and Shape in Relation to Refractive Error in Children:A Magnetic Resonance Imaging Study
Purpose: The purpose of this study was to determine the association between eye shape and volume measured with magnetic resonance imaging (MRI) and optical biometry and with spherical equivalent (SE) in children. Methods: For this study, there were 3637 10-year-old children from a population-based birth-cohort study that underwent optical biometry (IOL-master 500) and T2-weighted MRI scanning (height, width, and volume). Cycloplegic refractive error was determined by automated refraction. The MRI images of the eyes were segmented using an automated algorithm combining atlas registration with voxel classification. Associations among optical biometry, anthropometry, MRI measurements, and RE were tested using Pearson correlation. Differences between refractive error groups were tested using ANOVA. Results: The mean volume of the posterior segment was 6350 (±680) mm3. Myopic eyes (SE †-0.5 diopters [D]) had 470 mm3 (P < 0.001) and 970 mm3 (P < 0.001) larger posterior segment volume than emmetropic and hyperopic eyes (SE ℠+2.0D), respectively. The majority of eyes (77.1%) had an oblate shape, but 47.4% of myopic eyes had a prolate shape versus 3.9% of hyperopic eyes. The correlation between SE and MRI-derived posterior segment length (r -0.51, P < 0.001) was stronger than the correlation with height (r -0.30, P < 0.001) or width of the eye (r -0.10, P < 0.001). Conclusions: In this study, eye shape at 10 years of age was predominantly oblate, even in eyes with myopia. Of all MRI measurements, posterior segment length was most prominently associated with SE. Whether eye shape predicts future myopia development or progression should be investigated in longitudinal studies.</p
Eye Size and Shape in Relation to Refractive Error in Children:A Magnetic Resonance Imaging Study
Purpose: The purpose of this study was to determine the association between eye shape and volume measured with magnetic resonance imaging (MRI) and optical biometry and with spherical equivalent (SE) in children. Methods: For this study, there were 3637 10-year-old children from a population-based birth-cohort study that underwent optical biometry (IOL-master 500) and T2-weighted MRI scanning (height, width, and volume). Cycloplegic refractive error was determined by automated refraction. The MRI images of the eyes were segmented using an automated algorithm combining atlas registration with voxel classification. Associations among optical biometry, anthropometry, MRI measurements, and RE were tested using Pearson correlation. Differences between refractive error groups were tested using ANOVA. Results: The mean volume of the posterior segment was 6350 (±680) mm3. Myopic eyes (SE †-0.5 diopters [D]) had 470 mm3 (P < 0.001) and 970 mm3 (P < 0.001) larger posterior segment volume than emmetropic and hyperopic eyes (SE ℠+2.0D), respectively. The majority of eyes (77.1%) had an oblate shape, but 47.4% of myopic eyes had a prolate shape versus 3.9% of hyperopic eyes. The correlation between SE and MRI-derived posterior segment length (r -0.51, P < 0.001) was stronger than the correlation with height (r -0.30, P < 0.001) or width of the eye (r -0.10, P < 0.001). Conclusions: In this study, eye shape at 10 years of age was predominantly oblate, even in eyes with myopia. Of all MRI measurements, posterior segment length was most prominently associated with SE. Whether eye shape predicts future myopia development or progression should be investigated in longitudinal studies.</p
Identifying Human Disease Genes through Cross-Species Gene Mapping of Evolutionary Conserved Processes
Understanding complex networks that modulate development in humans is hampered by genetic and phenotypic heterogeneity within and between populations. Here we present a method that exploits natural variation in highly diverse mouse genetic reference panels in which genetic and environmental factors can be tightly controlled. The aim of our study is to test a cross-species genetic mapping strategy, which compares data of gene mapping in human patients with functional data obtained by QTL mapping in recombinant inbred mouse strains in order to prioritize human disease candidate genes.We exploit evolutionary conservation of developmental phenotypes to discover gene variants that influence brain development in humans. We studied corpus callosum volume in a recombinant inbred mouse panel (C57BL/6JĂDBA/2J, BXD strains) using high-field strength MRI technology. We aligned mouse mapping results for this neuro-anatomical phenotype with genetic data from patients with abnormal corpus callosum (ACC) development.).This approach that exploits highly diverse mouse strains provides an efficient and effective translational bridge to study the etiology of human developmental disorders, such as autism and schizophrenia
Mechanical properties of freely suspended atomically thin dielectric layers of mica
We have studied the elastic deformation of freely suspended atomically thin
sheets of muscovite mica, a widely used electrical insulator in its bulk form.
Using an atomic force microscope, we carried out bending test experiments to
determine the Young's modulus and the initial pre-tension of mica nanosheets
with thicknesses ranging from 14 layers down to just one bilayer. We found that
their Young's modulus is high (190 GPa), in agreement with the bulk value,
which indicates that the exfoliation procedure employed to fabricate these
nanolayers does not introduce a noticeable amount of defects. Additionally,
ultrathin mica shows low pre-strain and can withstand reversible deformations
up to tens of nanometers without breaking. The low pre-tension and high Young's
modulus and breaking force found in these ultrathin mica layers demonstrates
their prospective use as a complement for graphene in applications requiring
flexible insulating materials or as reinforcement in nanocomposites.Comment: 9 pages, 5 figures, selected as cover of Nano Research, Volume 5,
Number 8 (2012
- âŠ