| 492871. |
- Kozachenko, Andriy, et al.
(författare)
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Influence of the surfaces on the nucleation process during the cholesteric –nematic transition
- 2004
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Ingår i: Mol.Cryst.Liq.Cryst.. - 1542-1406. ; 412, s. 205/[1815]-218/[1828]
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Tidskriftsartikel (refereegranskat)abstract
- The nucleation phenomenon in short pitch cholesteric liquid crystals (LC), taking place during the relaxation from the electric field-induced cholesteric-nematic (CN) transition, has been investigated for various boundary conditions. The dynamic hysteresis properties have been studied by direct optical methods. For the first time it is shown the strong evidences that the nucleation is not exceptionally a bulk phenomenon and the supporting solid surfaces may act as nucleation sites. It is confirmed also that the nucleation velocity is not a function of the type of molecular alignment at the liquid crystal/solid interface rather than it depends on the uniformity of the surface interactions with liquid crystal molecules. This result is of importance for time scale optimization in modern fast driving schemes for cholesteric LCDs.
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| 492872. |
- Kozachkov, Leo, et al.
(författare)
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Achieving stable dynamics in neural circuits
- 2020
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Ingår i: PloS Computational Biology. - : Public Library of Science (PLoS). - 1553-734X .- 1553-7358. ; 16:8
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Tidskriftsartikel (refereegranskat)abstract
- The brain consists of many interconnected networks with time-varying, partially autonomous activity. There are multiple sources of noise and variation yet activity has to eventually converge to a stable, reproducible state (or sequence of states) for its computations to make sense. We approached this problem from a control-theory perspective by applying contraction analysis to recurrent neural networks. This allowed us to find mechanisms for achieving stability in multiple connected networks with biologically realistic dynamics, including synaptic plasticity and time-varying inputs. These mechanisms included inhibitory Hebbian plasticity, excitatory anti-Hebbian plasticity, synaptic sparsity and excitatory-inhibitory balance. Our findings shed light on how stable computations might be achieved despite biological complexity. Crucially, our analysis is not limited to analyzing the stability of fixed geometric objects in state space (e.g points, lines, planes), but rather the stability of state trajectories which may be complex and time-varying.
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| 492873. |
- Kozachkov, L, et al.
(författare)
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Robust and brain-like working memory through short-term synaptic plasticity
- 2022
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Ingår i: PLoS computational biology. - : Public Library of Science (PLoS). - 1553-7358. ; 18:12, s. e1010776-
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Tidskriftsartikel (refereegranskat)abstract
- Working memory has long been thought to arise from sustained spiking/attractor dynamics. However, recent work has suggested that short-term synaptic plasticity (STSP) may help maintain attractor states over gaps in time with little or no spiking. To determine if STSP endows additional functional advantages, we trained artificial recurrent neural networks (RNNs) with and without STSP to perform an object working memory task. We found that RNNs with and without STSP were able to maintain memories despite distractors presented in the middle of the memory delay. However, RNNs with STSP showed activity that was similar to that seen in the cortex of a non-human primate (NHP) performing the same task. By contrast, RNNs without STSP showed activity that was less brain-like. Further, RNNs with STSP were more robust to network degradation than RNNs without STSP. These results show that STSP can not only help maintain working memories, it also makes neural networks more robust and brain-like.
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| 492874. |
- Kozadaeva, M., et al.
(författare)
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Assessment of Microstructural, Mechanical and Electrochemical Properties of Ti–42Nb Alloy Manufactured by Electron Beam Melting
- 2023
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Ingår i: Materials. - : MDPI. - 1996-1944 .- 1996-1944. ; 16:13
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Tidskriftsartikel (refereegranskat)abstract
- The β-type Ti–42Nb alloy has been successfully manufactured from pre-alloyed powder using the E-PBF method for the first time. This study presents thorough microstructural investigations employing diverse methodologies such as EDS, XRD, TEM, and EBSD, while mechanical properties are assessed using UPT, nanoindentation, and compression tests. Microstructural analysis reveals that Ti–42Nb alloy primarily consisted of the β phase with the presence of a small amount of nano-sized α″-martensite formed upon fast cooling. The bimodal-grained microstructure of Ti–42Nb alloy comprising epitaxially grown fine equiaxed and elongated equiaxed β-grains with an average grain size of 40 ± 28 µm exhibited a weak texture. The study shows that the obtained microstructure leads to improved mechanical properties. Young’s modulus of 78.69 GPa is significantly lower than that of cp-Ti and Ti–6Al–4V alloys. The yield strength (379 MPa) and hardness (3.2 ± 0.5 GPa) also meet the criteria and closely approximate the values typical of cortical bone. UPT offers a reliable opportunity to study the nature of the ductility of the Ti–42Nb alloy by calculating its elastic constants. XPS surface analysis and electrochemical experiments demonstrate that the better corrosion resistance of the alloy in SBF is maintained by the dominant presence of TiO2 and Nb2O5. The results provide valuable insights into the development of novel low-modulus Ti–Nb alloys, which are interesting materials for additive-manufactured implants with the desired properties required for their biomedical applications.
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| 492875. |
- Kozak, Igor, et al.
(författare)
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Teleophthalmology image-based navigated retinal laser therapy for diabetic macular edema : a concept of retinal telephotocoagulation
- 2017
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Ingår i: Graefe's Archive for Clinical and Experimental Ophthalmology. - : Springer Science and Business Media LLC. - 0721-832X .- 1435-702X. ; 255:8, s. 1509-1513
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Tidskriftsartikel (refereegranskat)abstract
- Background: To determine the feasibility and efficacy of a retinal telephotocoagulation treatment plan for diabetic macular edema. Methods: Prospective, interventional cohort study at two clinical sites. Sixteen eyes of ten subjects with diabetic macular edema underwent navigated focal laser photocoagulation using a novel teleretinal treatment plan. Clinic 1 (King Khaled Eye Specialist Hospital, Riyadh, Saudi Arabia) collected retinal images and fundus fluorescein angiogram. Clinic 2 (Palmetto Retina Center, West Columbia, SC, USA) created image-based treatment plans based on which macular laser photocoagulation was performed back at clinic 1. The primary outcome of the study was feasibility of image transfer and performing navigated laser photocoagulation for subjects with diabetic macular edema between two distant clinics. Secondary measures were change in best-corrected visual acuity (BCVA) and central retinal thickness (CRT) by spectral-domain optical coherence tomography at 3 months after treatment. Results: The teleretinal treatment plan was able to be successfully completed in all 16 eyes. The mean logMAR BCVA at baseline was 0.49 ± 0.1, which remained stable (0.45 ± 0.1) 3 months after treatment (p = 0.060). The CRT improved from 290.1 ± 37.6 μm at baseline to 270.8 ± 27.7 μm 3 months after treatment (p = 0.005). All eyes demonstrated improvement in the area of retinal edema after laser photocoagulation, and no eyes demonstrated visual acuity loss 3 months after treatment. Conclusion: This study introduces the concept of retinal telephotocoagulation for diabetic macular edema, and demonstrates the feasibility and safety of using telemedicine to perform navigated retinal laser treatments regardless of geographical distance.
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| 492876. |
- Kozak, John J., et al.
(författare)
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Geometrical Description of Protein Structural Motifs
- 2018
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 122:49, s. 11289-11294
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Tidskriftsartikel (refereegranskat)abstract
- We present a geometrical method that can identify secondary structural motifs in proteins via angular correlations. The method uses crystal structure coordinates to calculate angular and radial signatures of each residue relative to an external reference point as the number of nearest-neighbor residues increases. We apply our approach to the blue copper protein amicyanin using the copper cofactor as the external reference point. We define a signature termed Δβ which describes the change in angular correlation as the span of nearest neighbor residues increases. We find that three turn regions of amicyanin harbor residues with Δβ near zero, while residues in other secondary structures have Δβ greater than zero: for β-strands, Δβ changes gradually residue by residue along the strand. Extension of our analysis to other blue copper proteins demonstrated that the noted structural trends are general. Importantly, our geometrical description of the folded protein accounts for all forces holding the structure together. Through this analysis, we identified some of the turns in amicyanin as symmetrical anchor points.
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| 492877. |
- Kozak, Ksenia, et al.
(författare)
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Evaluation of lane departure warnings for drowsy drivers
- 2006
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Ingår i: Proceedings of the Human Factors and Ergonomics Society 50th Annual Meeting. ; , s. 2400-2404
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Konferensbidrag (refereegranskat)abstract
- Lane departure warning (LDW) is a driver warning system designed to reduce the number of unintended lane departures. We addressed warning effectiveness and customer acceptance when the unintended lane departures are the result of drowsy driving. Thirty-two adults who were sleep deprived for 23 hours participated in the study and drove Ford's VIRTTEX driving simulator. Four Human Machine Interfaces (HMI) for LDW were evaluated: Steering Wheel Torque, Rumble Strip Sound, Steering Wheel Vibration and Head Up Display. A yaw deviation technique was used to produce controlled lane departures in the first two hours of the drive while for the last 20 minutes driver-initiated lane departures were analyzed. The Steering Wheel Vibration HMI, accompanied by Steering Wheel Torque, was found to be the most effective HMI for LDW in a group of drowsy drivers, with faster reaction times and smaller lane excursions. The Vibration HMI was also perceived by the drowsy drivers to be acceptable and helpful.
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| 492878. |
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| 492879. |
- Kozak Ljunggren, Monika, et al.
(författare)
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Effect of Surgical Technique on Corneal Implant Performance.
- 2014
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Ingår i: Translational Vision Science & Technology. - : Association for Research in Vision and Ophthalmology (ARVO). - 2164-2591. ; 3:2
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: Our aim was to determine the effect of a surgical technique on biomaterial implant performance, specifically graft retention.METHODS: Twelve mini pigs were implanted with cell-free, 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS) cross-linked recombinant human collagen type III (RHCIII) hydrogels as substitutes for donor corneal allografts using overlying sutures with or without human amniotic membrane (HAM) versus interrupted sutures with HAM. The effects of the retention method were compared as well as the effects of collagen concentration (13.7% to 15% RHCIII).RESULTS: All implanted corneas showed initial haze that cleared with time, resulting in corneas with optical clarity matching those of untreated controls. Biochemical analysis showed that by 12 months post operation, the initial RHCIII implants had been completely remodeled, as type I collagen, was the major collagenous protein detected, whereas no RHCIII could be detected. Histological analysis showed all implanted corneas exhibited regeneration of epithelial and stromal layers as well as nerves, along with touch sensitivity and tear production. Most neovascularization was seen in corneas stabilized by interrupted sutures.CONCLUSIONS: This showed that the surgical technique used does have a significant effect on the overall performance of corneal implants, overlying sutures caused less vascularization than interrupted sutures.TRANSLATIONAL RELEVANCE: Understanding the significance of the suturing technique can aid the selection of the most appropriate procedure when implanting artificial corneal substitutes. The same degree of regeneration, despite a higher collagen content indicates that future material development can progress toward stronger, more resistant implants.
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| 492880. |
- Kozak, M, et al.
(författare)
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Expression of a selenomethionine derivative and preliminary crystallographic studies of human cystatin C
- 1999
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Ingår i: Acta Crystallographica. Section D: Biological Crystallography. - 1399-0047. ; 55:11, s. 1939-1942
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Tidskriftsartikel (refereegranskat)abstract
- Human cystatin C, a protein with amyloidogenic properties and a potent inhibitor of papain-like mammalian proteases, has been produced in its full-length form by recombinant techniques and crystallized in two polymorphic forms: cubic and tetragonal. A selenomethionyl derivative of the protein, obtained by Escherichia coli expression and with complete Met→Se-Met substitution confirmed by mass spectrometry, amino-acid analysis and X-ray absorption spectra, was crystallized in the cubic form. A truncated variant of the protein, lacking ten N-terminal residues, has also been crystallized. The crystals of this variant are tetragonal and, like the two polymorphs of the full-length protein, contain multiple copies of the molecule in the asymmetric unit, suggesting oligomerization of the protein.
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