6,185 research outputs found
Recent advances in 3D printing of biomaterials.
3D Printing promises to produce complex biomedical devices according to computer design using patient-specific anatomical data. Since its initial use as pre-surgical visualization models and tooling molds, 3D Printing has slowly evolved to create one-of-a-kind devices, implants, scaffolds for tissue engineering, diagnostic platforms, and drug delivery systems. Fueled by the recent explosion in public interest and access to affordable printers, there is renewed interest to combine stem cells with custom 3D scaffolds for personalized regenerative medicine. Before 3D Printing can be used routinely for the regeneration of complex tissues (e.g. bone, cartilage, muscles, vessels, nerves in the craniomaxillofacial complex), and complex organs with intricate 3D microarchitecture (e.g. liver, lymphoid organs), several technological limitations must be addressed. In this review, the major materials and technology advances within the last five years for each of the common 3D Printing technologies (Three Dimensional Printing, Fused Deposition Modeling, Selective Laser Sintering, Stereolithography, and 3D Plotting/Direct-Write/Bioprinting) are described. Examples are highlighted to illustrate progress of each technology in tissue engineering, and key limitations are identified to motivate future research and advance this fascinating field of advanced manufacturing
Qualitative picture of a new mechanism for high-Tc superconductors
Xu et al. observed enhanced Nernst effect and Iguchi et al. observed patched
diamagnetism, both well above in underdoped high- superconductors
(HTSCs). A new mechanism is proposed here, which seems to naturally explain, at
least qualitatively, these observations, as well as the d-wave nature and
continuity of pseudogap and pairing gap, the tunneling conductance above ,
as well as , , , etc. This mechanism combines
features of dynamic charged stripes, preformed pairs, and spin-bags: At
appropriete doping levels, the doped holes (and perhaps also electrons) will
promote the formation of anti-phase islands in short-range anti-ferromagnetic
order. On the boundary of each such island reside two doped carriers; the
unscreened Coulomb repulsion between them stabilizes its size.
Superconductivity results when such ``pre-formed pairs'' Bose-condense.Comment: 8 pages, 4 figures, New3SC-4 Conference Proceedings, to be published
in ijmp
Neutrino Masses in a 5D TeV Unification Model
We study the generation of neutrino masses in the electroweak
unified theory in spacetime. By appropriate
orbifolding, the bulk symmetry is broken into
at one of the fixed points, where the quarks reside. The leptons form
triplets, localized at the other symmetric fixed point. The fermion masses
arise from the bulk Higgs sector containing a triplet and an anti-sextet. We
construct neutrino Majorana masses via 1-loop quantum corrections by adding a
parity odd bulk triplet scalar. No right-handed neutrino is needed. The
neutrino mass matrix is of the inverted hierarchy type. We show that the model
can easily accommodate the bi-large mixing angle solution favored by the recent
neutrino experiments without much fine tuning of parameters. The constraints
from \mu\ra 3e transition and neutrinoless double beta decays are discussed.Comment: 14 pages, 4 figure
A quantitative assessment of empirical magnetic field models at geosynchronous orbit during magnetic storms
[1] We evaluate the performance of recent empirical magnetic field models (Tsyganenko, 1996, 2002a, 2002b; Tsyganenko and Sitnov, 2005, hereafter referred to as T96, T02 and TS05, respectively) during magnetic storm times including both pre- and post-storm intervals. The model outputs are compared with GOES observations of the magnetic field at geosynchronous orbit. In the case of a major magnetic storm, the T96 and T02 models predict anomalously strong negative Bz at geostationary orbit on the nightside due to input values exceeding the model limits, whereas a comprehensive magnetic field data survey using GOES does not support that prediction. On the basis of additional comparisons using 52 storm events, we discuss the strengths and limitations of each model. Furthermore, we quantify the performance of individual models at predicting geostationary magnetic fields as a function of local time, Dst, and storm phase. Compared to the earlier models (T96 and T02), the most recent storm-time model (TS05) has the best overall performance across the entire range of local times, storm levels, and storm phases at geostationary orbit. The field residuals between TS05 and GOES are small (≤3 nT) compared to the intrinsic short time-scale magnetic variability of the geostationary environment even during non-storm conditions (∼24 nT). Finally, we demonstrate how field model errors may affect radiation belt studies when estimating electron phase space density
Adenovirus-mediated gene transfer to liver grafts: An improved method to maximize infectivity
Background. Adenoviral gene therapy in liver transplantation has many potential applications, but current vector delivery methods to grafts lack efficiency and require high titers. In this study, we attempted to improve gene delivery efficacy using three different delivery methods to liver grafts with adenoviral vector encoding the LacZ marker gene (AdLacZ). Methods. AdLacZ was delivered to cold preserved rat liver grafts by: (1) continuous perfusion via the portal vein (portal perfusion), (2) continuous perfusion via both the portal vein and hepatic artery (dual perfusion), and (3) trapping viral perfusate in the liver vasculature by clamping outflow (clamp technique). Results. Using 1x109 plaque-forming units of Ad-LacZ (multiplicity of infection of 0.4), transduction rate in 3-hr preserved liver grafts, determined by 5-bromo-4-chromo-3-indolyl-β-D-galactopyranoside staining and β-galactosidase assay 48 hr after transplantation, was best with clamp technique (21.5±2.7% 5-bromo-4-chromo-3-indolyl-β-D- galactopyranoside-positive cells and 81.1±3.6 U/g β-galactosidase), followed by dual perfusion (18.5±1.8%, 66.6±19.4 U/g) and portal perfusion (8.8±2.5%, 19.7±15.4 U/g). Further studies using clamp technique demonstrated a near-maximal gene transfer rate of 30% at multiplicity of infection of 0.4 with prolonged cold ischemia to 18 hr. Transgene expression was stable for 2 weeks and slowly declined to 7.8±12.1% at day 28. Lack of inflammatory response was confirmed by histopathological examination and liver enzymes. Transduction was selectively induced in hepatocytes with nearly no extrahepatic transgene expression in the lung and spleen. Conclusions. The clamp technique provides a highly efficient viral gene delivery method to cold preserved liver grafts. This method offers maximal infectivity of adenoviral vector with minimal technical manipulation
Cellular Ability to Sense Spatial Gradients in the Presence of Multiple Competitive Ligands
Many eukaryotic and prokaryotic cells can exhibit remarkable sensing ability
under small gradient of chemical compound. In this study, we approach this
phenomenon by considering the contribution of multiple ligands to the chemical
kinetics within Michaelis-Menten model. This work was inspired by the recent
theoretical findings from Bo Hu et al. [Phys. Rev. Lett. 105, 048104 (2010)],
our treatment with practical binding energies and chemical potential provides
the results which are consistent with experimental observations.Comment: 5 pages, 4 figure
Social media and orthodontics – are our patients scrolling?
OBJECTIVE: To assess patients’ awareness of the availability of information related to orthodontics on social media, and to explore patients’ willingness to engage with social media to aid with orthodontic treatment. DESIGN: Prospective cross-sectional survey. SETTING: This survey was conducted at Croydon University Hospital orthodontic department. PARTICIPANTS: A total of 125 orthodontic patients, both new and in treatment. There were no exclusion criteria. METHODS: All participants completed a questionnaire designed to explore their awareness, access to and utilisation of social media as well as their willingness to engage with social media to support orthodontic treatment. There were no age restrictions or exclusion criteria. RESULTS: Of the patients, 99% had access to social media. Of these patients, 64% were aware that social media platforms were available to help with orthodontic treatment, 30% had utilised social media related to orthodontics, with the most popular platforms being Instagram (n = 17) and Snapchat (n = 12). Of the patients, 73% stated that they would be willing to use social media in the future to support orthodontic treatment. CONCLUSION: Social media can be engaging, accessible and versatile, and has been shown to be effective at improving patients’ knowledge regarding orthodontic treatment. As such, it may be used as a valuable tool for information provision to engage orthodontic patients. Awareness of the availability of orthodontics content on social media is increasing; however, only one-third of participants had previously used it to aid with orthodontic treatment. Given the availability of information on social media targeted at orthodontic patients there is a need to assess the quality of this information and if appropriate navigate patients towards high-quality, effective resources
Heliospheric plasma sheets
[1] As a high-beta feature on scales of hours or less, the heliospheric plasma sheet (HPS) encasing the heliospheric current sheet shows a high degree of variability. A study of 52 sector boundaries identified in electron pitch angle spectrograms in Wind data from 1995 reveals that only half concur with both high-beta plasma and current sheets, as required for an HPS. The remaining half lack either a plasma sheet or current sheet or both. A complementary study of 37 high-beta events reveals that only 5 contain sector boundaries while nearly all (34) contain local magnetic field reversals, however brief. We conclude that high-beta plasma sheets surround current sheets but that most of these current sheets are associated with fields turned back on themselves. The findings are consistent with the hypothesis that high-beta plasma sheets, both at and away from sector boundaries, are the heliospheric counterparts of the small coronal transients observed at the tips of helmet streamers, in which case the proposed mechanism for their release, interchange reconnection, could be responsible for the field inversions
Probing the superconducting gap symmetry of PrRuSb: A comparison with PrOsSb
We report measurements of the magnetic penetration depth in single
crystals of PrRuSb down to 0.1 K. Both and superfluid
density exhibit an exponential behavior for 0.5, with
parameters (0)/\textit{k}\textit{T} = 1.9 and
= 2900 \AA. The value of (0) is consistent with the specific-heat jump
value of = 1.87 measured elsewhere, while the value of
is consistent with the measured value of the electronic
heat-capacity coefficient . Our data are consistent with
PrRuSb being a moderate-coupling, fully-gapped superconductor. We
suggest experiments to study how the nature of the superconducting state
evolves with increasing Ru substitution for Os
Entangled-State Cycles of Atomic Collective-Spin States
We study quantum trajectories of collective atomic spin states of
effective two-level atoms driven with laser and cavity fields. We show that
interesting ``entangled-state cycles'' arise probabilistically when the (Raman)
transition rates between the two atomic levels are set equal. For odd (even)
, there are () possible cycles. During each cycle the
-qubit state switches, with each cavity photon emission, between the states
, where is a Dicke state in a rotated
collective basis. The quantum number (), which distinguishes the
particular cycle, is determined by the photon counting record and varies
randomly from one trajectory to the next. For even it is also possible,
under the same conditions, to prepare probabilistically (but in steady state)
the Dicke state , i.e., an -qubit state with excitations,
which is of particular interest in the context of multipartite entanglement.Comment: 10 pages, 9 figure
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