Optical Center Research Articles

Rapamycin Improved Retinal Function and Morphology in a Mouse Model of Retinal Degeneration.

The retina is an important visual organ, which is responsible for receiving light signals and transmitting them to the optic nerve center step by step. The retina contains a variety of cells, among which photoreceptor cells receive light signals and convert them into nerve signals, and are mainly responsible for light and dark vision. Retinal degeneration is mainly the degeneration of photoreceptor cells, and retinitis pigmentosa (RP) is characterized by rod degeneration followed by cone degeneration. So far, there is still a lack of effective drugs to treat RP. Here, we established a stable RP model by tail vein injection of methyl methanesulfonate to study the mechanism of retinal photoreceptor degeneration. Mechanistic target of rapamycin (mTOR) is located in the central pathway of growth and energy metabolism and changes in a variety of diseases in response to pathological changes. We found that the mTOR was activated in this model. Therefore, the inhibitor of mTOR, rapamycin was used to suppress the expression of mTOR and interfere with photoreceptor degeneration. Electroretinogram assay showed that the function of mice retina was improved. Hematoxylin and eosin staining results displayed that retinal photoreceptor thickness and morphology were improved. Also, the autophagy in rapamycin group was activated, which revealed that rapamycin may protect the retinal photoreceptor by inhibiting mTOR and then activating autophagy.

A repeating fast radio burst source in a globular cluster.

Fast radio bursts (FRBs) are flashes of unknown physical origin1. The majority of FRBs have been seen only once, although some are known to generate multiple flashes2,3. Many models invoke magnetically powered neutron stars (magnetars) as the source of the emission4,5. Recently, the discovery6 of another repeater (FRB 20200120E) was announced, in the direction of the nearby galaxy M81, with four potential counterparts at other wavelengths6. Here we report observations that localized the FRB to a globular cluster associated with M81, where it is 2 parsecs away from the optical centre of the cluster. Globular clusters host old stellar populations, challenging FRB models that invoke young magnetars formed in a core-collapse supernova. We propose instead that FRB 20200120E originates from a highly magnetized neutron star formed either through the accretion-induced collapse of a white dwarf, or the merger of compact stars in a binary system7. Compact binaries are efficiently formed inside globular clusters, so a model invoking them could also be responsible for the observed bursts.

Optical Studies in Red/NIR Persistent Luminescent Cr-Doped Zinc Gallogermanate (ZGGO:Cr)

Zn1+xGa2−2xGexO4 (ZGGO:Cr)-persistent phosphor, with a molar fraction, x, of x = 0.1, doped with a 0.5% molar of chromium, was synthesised via solid-state reaction at 1350 °C for 36 h. X-ray diffraction measurements and Raman spectroscopy evidence a single crystalline phase corresponding to the cubic spinel structure. Room temperature (RT) photoluminescence (PL) and afterglow decay profiles were investigated using above and below bandgap excitation. In both cases, persistent PL was observed for almost 8 h, mainly originating from a Cr3+ defect, the so-called N2 optical centre. RT PL excitation and diffuse reflectance allow identification of the best pathways of Cr3+ red/NIR emission, as well as estimation of the ZGGO bandgap energy at 4.82 eV. An in-depth investigation of the observed luminescence at 15 K and temperature-dependent PL under site-selective excitation reveals the spectral complexity of the presence of several optically active Cr3+ centres in the ZGGO host that emit in almost the same spectral region. Furthermore, the temperature dependence of the R-lines’ intensity indicates the existence of thermal populating processes between the different optical centres. Such observations well account for a wide distribution of defect trap levels available for carrier capture/release, as measured by the persistent luminescence decay, from which the carriers are released preferentially to the N2 Cr3+-related optical centre.

Carbon Dots with an Emission in the Near Infrared Produced from Organic Dyes in Porous Silica Microsphere Templates.

Carbon dots (CDs) with an emission in the near infrared spectral region are attractive due to their promising applications in bio-related areas, while their fabrication still remains a challenging task. Herein, we developed a template-assisted method using porous silica microspheres for the formation of CDs with optical transitions in the near infrared. Two organic dyes, Rhodamine 6G and IR1061 with emission in the yellow and near infrared spectral regions, respectively, were used as precursors for CDs. Correlation of morphology and chemical composition with optical properties of obtained CDs revealed the origin of their emission, which is related to the CDs’ core optical transitions and dye-derivatives within CDs. By varying annealing temperature, different kinds of optical centers as derivatives of organic dyes are formed in the microsphere’s pores. The template-assisted method allows us to synthesize CDs with an emission peaked at 1085 nm and photoluminescence quantum yield of 0.2%, which is the highest value reported so far for CDs emitting at wavelengths longer than 1050 nm.

Study of the photoluminescence of N-doped, Carbon Dot-based nanocomposite materials from citric acid and urea

In this work, we investigate the photoluminescence mechanisms of N-doped, CQD-based nanocomposites, in the form of aqueous suspensions as well as the transition to thin films, in order to facilitate their use for solid-state applications. The products of two different synthetic routes have been investigated for their optical response in the form of aqueous suspensions and thin films. In addition, dialysis was utilized to purify and separate the as-synthesized material into different fractions, which were then studied separately. The PL spectra revealed two optical centers identified as H-aggregates of citrazinic acid derivatives and 4-hydroxy-1H-pyrrolo[3,4-c]pyridine-1,3,6(2H,5H)-trione (HPPT). The materials were further studied with FTIR and UV–Vis spectroscopy, as well as TEM microscopy, in order to acquire a better understanding of these optical centers. The optical centers were found to be excitation-independent emitters, sensitive to ambient pH conditions and able to interact with each other by an energy transfer mechanism in the solid state.

Formation energy and optical excitation mechanisms of Er in GaN semi-bulk crystals

Erbium (Er) doped GaN (Er:GaN) bulk crystals are promising as an optical gain material for high energy lasers. Other than the preferred configuration of Er3+ occupying the Ga site with four nearest neighbor N atoms (ErGa), Er can also form a complex with a defect (ErGa-DX) in Er:GaN. A set of Er:GaN semi-bulk crystals were grown by hydride vapor phase epitaxy (HVPE) at different growth temperatures to allow the determination of the formation energies, EF, of Er optical centers in Er:GaN. Photoluminescence (PL) emission spectra near 1.5 μm pumped by a near band edge excitation (λexc = 375 nm) and by a resonant excitation (λexc = 980 nm) were measured, which yielded two different formation energies of EF = 2.8 eV and 3.3 eV, corresponding to the formation of ErGa-DX and ErGa in Er:GaN, respectively. As a gain medium, the formation of ErGa-DX in Er:GaN would not only reduce the pumping efficiency of Er optical centers but also increase the optical loss. Our results provide useful insights into possible strategies for enhancing the fraction of ErGa in Er:GaN and, hence, the pumping efficiency, paving the way for achieving optical gain and lasing in Er:GaN.

Planar polarity in primate cone photoreceptors: a potential role in Stiles Crawford effect phototropism

Human cone phototropism is a key mechanism underlying the Stiles-Crawford effect, a psychophysiological phenomenon according to which photoreceptor outer/inner segments are aligned along with the direction of incoming light. However, such photomechanical movements of photoreceptors remain elusive in mammals. We first show here that primate cone photoreceptors have a planar polarity organized radially around the optical center of the eye. This planar polarity, based on the structure of the cilium and calyceal processes, is highly reminiscent of the planar polarity of the hair cells and their kinocilium and stereocilia. Secondly, we observe under super-high resolution expansion microscopy the cytoskeleton and Usher proteins architecture in the photoreceptors, which appears to establish a mechanical continuity between the outer and inner segments. Taken together, these results suggest a comprehensive cellular mechanism consistent with an active phototropism of cones toward the optical center of the eye, and thus with the Stiles-Crawford effect.

Calibration Method for Line-Structured Light Three-Dimensional Measurements Based on a Single Circular Target

Single circular targets are widely used as calibration objects during line-structured light three-dimensional (3D) measurements because they are versatile and easy to manufacture. This paper proposes a new calibration method for line-structured light 3D measurements based on a single circular target. First, the target is placed in several positions and illuminated by a light beam emitted from a laser projector. A camera captures the resulting images and extracts an elliptic fitting profile of the target and the laser stripe. Second, an elliptical cone equation defined by the elliptic fitting profile and optical center of the camera is established based on the projective geometry. By combining the obtained elliptical cone and the known diameter of the circular target, two possible positions and orientations of the circular target are determined and two groups of 3D intersection points between the light plane and the circular target are identified. Finally, the correct group of 3D intersection points is filtered and the light plane is progressively fitted. The accuracy and effectiveness of the proposed method are verified both theoretically and experimentally. The obtained results indicate that a calibration accuracy of 0.05 mm can be achieved for an 80 mm × 80 mm planar target.

Time-Resolved Photoionization Detection of a Single Er3+ Ion in Silicon.

The detection of charge trap ionization induced by resonant excitation enables spectroscopy on single Er3+ ions in silicon nanotransistors. In this work, a time-resolved detection method is developed to investigate the resonant excitation and relaxation of a single Er3+ ion in silicon. The time-resolved detection is based on a long-lived current signal with a tunable reset and allows the measurement under stronger and shorter resonant excitation in comparison to time-averaged detection. Specifically, the short-pulse study gives an upper bound of 23.7 μs on the decay time of the 4I13/2 state of the Er3+ ion. The fast decay and the tunable reset allow faster repetition of the single-ion detection, which is attractive for implementing this method in large-scale quantum systems of single optical centers. The findings on the detection mechanism and dynamics also provide an important basis for applying this technique to detect other single optical centers in solids.

Spectroscopy of the yttrium scandate doped by thulium ions

The thulium-doped yttrium scandate crystal fiber has been obtained by the laser-heated pedestal growth method. The crystal belongs to the bixbyite type, has a cubic structure and crystallizes in the Ia3 space group. The lattice parameters (a=10.224(1) Angstrem) have been determined using the powder X-ray diffraction. Spectral-kinetic measurements have allowed to detect two symmetrically independent optical centers of Tm3+ ions in the crystal fiber. Keywords: bixbyite, optical center, rare-earth ion, laser-heated pedestal growth.

A Fast Data Synchronization Technique in Optical Inter-Connected Data Centers

A Fast Data Synchronization Technique in Optical Inter-Connected Data Centers

The role of the macular interface in the diagnosis of retinopathy of prematurity on the «Key to Diagnosis I » platform

AbstractPurposeTo minimize the risk of medical error in the diagnosis and choice of treatment of ROP by improving the quality and analysis of modeled wide‐field images on the Key to Diagnosis I platform.Methods1278 RetCam images of ROP 272(544 eyes) were divided into 5 groups 1‐I stage 152(304 eyes), 2‐II stage 45(90 eyes), 3‐III stage 8(12 eyes), 4‐posterior aggressive ROP 7(14 eyes), 5‐retinal immaturity 60(120 eyes); A standard clinical examination, analysis of wide‐field retinal images, macula localization and traction index of the macular region (Tm) calculation were performed. Tm is a leght‐to‐width attitude of ellipse goes through the center of optic nerve head and arcades.ResultsPlatform modules have been developed for automatic modeling of wide‐field retinal images and localization of the macula, which is a reference point for centering wide‐field images and assessing the extent of pathological changes. In the ROP group, a significant inverse correlation was observed between the values of Tm, 1A‐0.8 ± 0.03, 1B‐0.75 ± 0.04, 1B‐0.74 ± 0.13, 1D‐0.99 ± 0.01, 1D‐0.91 ± 0.09.DiscussionThe macular area can be described by ellipse, which form correlate with refraction [1]. The influence of the traction component on the macular zone connected with decrease in refractive pathology in the treatment Anti‐vascular endothelial growth factor [2].ConclusionsAt ROP Tm reflects the severity of traction processes at the retina periphery and marks the severity of pathology in case of diagnostic defects. The macula localization determines the stable points: the optic nerve disc physiological excavation center, temporal arcades and the macula circumference for photogrammetry of 3D eye model. Hill D. Retinal characteristics of myopic eyes in a semi‐rural UK population. Diss. Aston University, 2019. Sankar M. J., Sankar J., Chandra P. Anti‐vascular endothelial growth factor drugs for treatment of retinopathy of prematurity. Cochrane Database of Systematic Reviews. 2018; 1.

Disc-fovea distance and choroidal thickness: is there a relationship?

Background:The distance between the optic disc center and the fovea is a biometric parameter; however, it is unclear whether DFD (disc–fovea distance) affects the choroidal thickness.Objective:The aim of this study is to investigate the association between DFD and choroidal thickness.Design:This is a prospective, and cross-sectional study.Methods:Two hundred fifty eyes of 250 healthy participants were examined in terms of DFD, age, axial length, spherical equivalent, and choroidal thickness. Inclusion criteria included aged between 20–40 years, no posterior segment disorders, and participants with best-corrected visual acuity (10/10 according to Snellen’s chart). Participants with high hypermetropia (>4 diopter) or myopia (>6 diopter) or any systemic disease likely to affect choroidal thickness were excluded. Choroidal thickness measurements were performed at subfoveal, 1.0 mm temporal, and 1.0 mm nasal using the enhanced-depth imaging optical coherence tomography.Results:The mean age of all the participants was 26.21 ± 5.73 years, mean DFD was 4634.29 ± 274.70 µm, mean axial length was 23.62 ± 0.83 mm, and mean spherical equivalent was −0.61 ± 1.06 diopter. The mean subfoveal, nasal, and temporal choroidal thicknesses were 388.73 ± 90.15 µm, 351.26 ± 88.09 µm, and 366.50 ± 79.56 µm, respectively. A negative correlation was found between subfoveal, nasal, and temporal choroidal thicknesses and axial length (r = −0.157, p = 0.013; r = −0.168, p = 0.008; r = −0.174, p = 0.006, respectively). Insignificant correlation was found between choroidal thicknesses and spherical equivalent (p > 0.05). There was not a statistically significant correlation between DFD and subfoveal, nasal, and temporal choroidal thicknesses (r = −0.028, p = 0.655; r = 0.030, p = 0.641; r = −0.025, p = 0.699, respectively). In addition, there was not a statistically significant correlation between age and choroidal thickness.Conclusion:This study shows that DFD and spherical equivalent do not affect choroidal thickness; axial length negatively affects choroidal thickness. In addition, age does not affect choroidal thickness between 20 and 40 years.

Calibration Method of Distance Between Optical Center of Camera and Rotation Axis in Rotating Vision Measurement System

Calibration Method of Distance Between Optical Center of Camera and Rotation Axis in Rotating Vision Measurement System

Efficient and Accurate Stitching for 360° Dual-Fisheye Images and Videos.

Back-to-back dual-fisheye cameras are the most cost-effective devices to capture 360° visual content. However, image and video stitching for such cameras often suffer from the effect of fisheye distortion, photometric inconsistency between the two views, and non-collocated optical centers. In this paper, we present algorithms for geometric calibration, photometric compensation, and seamless stitching to address these issues for back-to-back dual-fisheye cameras. Specifically, we develop a co-centric trajectory model for geometric calibration to characterize both intrinsic and extrinsic parameters of the fisheye camera to fifth-order precision, a photometric correction model for intensity and color compensation to provide efficient and accurate local color transfer, and a mesh deformation model along with an adaptive seam carving method for image stitching to reduce geometric distortion and ensure optimal spatiotemporal alignment. The stitching algorithm and the compensation algorithm can run efficiently for 1920×960 images. Quantitative evaluation of geometric distortion, color discontinuity, jitter, and ghost artifact of the resulting image and video shows that our solution outperforms the state-of-the-art techniques.

Developing optical up-conversion process via embedded silver nanostructures

Up-conversion optical process has been extensively used over the last two decades in different applications such as bioimaging, sensors, and optical energy harvesting, depending on converting lower energy photons into higher energy ones. There are different hosts acting as optical centers for up-conversion process, however erbium-doped-NaYF4 is one of the most promising used materials due to its relatively low-phonon environment. In this paper, the development of up-conversion efficiency is analytically studied through addition of silver nanostructures such as nanoparticles and nanorods. This work introduces the analysis of both luminescence and up-conversion efficiency changes of erbium-doped-NaYF4 (Er–NaYF4) according to the enhanced carriers population according to the added silver nanostructures. The results show that silver nanorodsin a higher efficiency improvement compared to the addition of nanoparticles.

Consequences of COVID-19 on my experiment of gene overexpression in beans

<p>My name is Salma Meléndez and I am currently a graduate in Agrogenomic Sciences. In March 2020, when COVID-19 was detected in Mexico, I was in my eighth semester of my undergraduate degree. At that time, he had an experiment of overexpression of a gene in bean roots, in order to explore its function during symbiosis with rhizobial bacteria. Unfortunately, the laboratory and the entire campus canceled their face-to-face activities in order to reduce the risk of contagion. An alternative was to take the experimental plants to my house to give the proper care, however, the situation became difficult as I did not have the space or the required conditions at home. On the other hand, other research centers with which we had collaboration agreements also canceled access, such is the case of the Optical Research Center, where we used the confocal microscope to detect subcellular location of proteins. The closure of institutions allowed me to write theoretical parts of my thesis, however, the experimental phase was definitely affected for at least six months. The experiment with the plants was almost completely lost. In the subsequent months I had the opportunity to re-enter my institution; however, under strict conditions and on staggered days, which made certain measurements that require daily continuity difficult. Currently, the laboratory is not as it used to look, full of colleagues sharing results and difficulties, exchanging advice and even certain materials. I think the pandemic has pushed us to do our work more individually and slowly. Consequently, my degree was delayed and transferred from 2020 to 2021. There are still many challenges to overcome, although activities have not been fully restored, science does not stop and we have found a way to face it, slowly but surely.</p>

Measurement and Analysis of Whole-surface Power Distribution in Single Tilted Spectacle Lenses.

Face-form tilt spectacles are sometimes tilted such that the optical properties of the embedded prescription lenses and the lens power change. If the lens power is not plano, the vision quality of the wearer may be affected. This study aimed to measure the whole-surface power distributions of tilted spectacle lenses for different lens powers and tilt angles. Spherical spectacle lenses with a refractive index of 1.56 and powers of -4.00 D, -2.00 D, plano, +2.00 D, and +4.00 D were measured. Their whole-surface power distributions were measured at different tilt angles, up to 20°, using a commercially available Hartmann wavefront aberrometer. The measured data were limited within a 40-mm diameter and analyzed to obtain contour plots of the spherical equivalent (M) and astigmatism (J). The measured whole-surface power profiles of the nontilted lenses showed both M and J as being symmetrical and increasing outward up to -0.52 and +0.24 D, respectively, for the -4.00 D lens and +0.22 and +0.05 D, respectively, for the +4.00 D lens, corresponding to the spherical design. The profiles of the tilted lenses showed both M and J as unevenly increasing from the center to the peripheral area along the downward tilt direction; however, the plano lens exhibited no effect of tilt on both M and J. The powers at the optical center of the lens increased with tilt angle and lens power. The maximum differences for M and J at a 15° tilt angle in the -4.00 D lens were -2.46 and +1.43 D, respectively. Conversely, at a 17° tilt angle, the maximum differences in the +4.00 D lens were +0.96 D in M and +0.46 D in J. Tilt angle and lens power strongly affect the power profiles of tilted spectacle lenses.

The Scope of Optometry Practice in Jordan.

The scope of optometry practice varies worldwide. Although the scope of optometry practice in Jordan is regulated, discrepancies exist in the services that optometry professionals provide. This study aimed to document the scope of optometry practice in Jordan and to describe the services that optometry professionals provide, as well as to inform regulatory bodies and educators about the current situation of optometry practice and areas that require development. A cross-sectional study was conducted using a questionnaire completed by optometry professionals working across Jordan. The questionnaire items cover the services and the tests they perform. Of the 714 participants, 57.8% were female and 42.2% were male, with a median age of 29 years. Participants were unevenly distributed across Jordan, with the majority working in the major cities and at optical centers (81.5%). Most participants were described as "refractionists." The most frequently provided services were basic optometric examinations, followed by community eye care services. Ocular medications were not prescribed by any participant. Reasons for not providing services were mainly attributed to license/profession regulations constraints and the service(s) not being part of the job description. About one-half of the participants have the knowledge to diagnose adnexal and anterior segment disorders. Optometry professionals in Jordan can provide more services if the scope of practice is expanded to match their knowledge and skills. Moreover, their nomenclature as refractionists does not represent the range of services they provide that extend beyond refraction. The concern is that optometric services are not reachable by many Jordanian populations because of the inequality of the distribution of professionals. Thus, advocacy to expand the scope of practice in Jordan is recommended.

Photoluminescence studies of optical centers generated by the B ion irradiation in Ib diamond

The photoluminescence (PL) spectra were employed to study the optical centers generated by the B ion irradiation in Ib diamond. The luminescent spectra with zero phonon lines (ZPLs) centered at 573, 575.8, 637.9, 390.8 nm and the most of the vibronic bands in vicinity of the ZPLs were detected using 532 and 325 nm lasers. The function of spot scan, surface scan and depth scan of Renishaw micro-Raman spectrometers were performed to understand spatial distribution of the resulting high density optical centers at 80 K. Through the spatial distribution of 575.8 and 637.9 nm optical centers, it was found that it’s more advantageous to form 575.8 nm optical centers for high density nitrogen diamond irradiated by B ion and subsequent annealing. Based on the principle of electrical neutrality and the degree of lattice distortion, it was proposed that a possible defect evolution process of the B-related optical center.