Neural development and regeneration in the visual system of teleosts

The structure of the developing optic tectum of the trout has been investigated using histological preparations and fresh material. The neuroblasts reached the pial surface and started to differentiate before separating from the ependymal processes. A new finding was the presence of inverted pear- shaped neurones in the plexiform external layer in Golgi sections of adult tectum. The organisation of the tectum was found to be similar to that described by Leghissa (1955).The first optokinetic responses occurred in trout embryos at a stage of development at which the thickness of the outer white zone was equal to that of the inner grey zone. The topographical representation of the visual field on the optic tectum of ten normal goldfish was mapped electro-physiologically using metal-filled micropipette electrodes.The topographical representation of the visual field on the optic tectum of ten normal goldfish was mapped electro- physiologically using metal -filled micropipette electrodes. Responses were evoked by visual stimulation with spots of light and with black discs of various sizes.Restoration of the visual projection over the right tectum following excision and reimplantation of the tectum in its normal orientation was studied in a series of goldfish at different times after the operation. There was a wide variation in the time taken for the restoration of the retinotectal projection map. From the third postoperative month some normal projections in the graft area were seen. It was concluded that optic nerve fibres can regenerate into the graft, and that the graft may retain its original specificities, viz. its specialization to represent a particular part of the retinaeCases where recovery occurred later than three months were those with larger areas of grafted tissue.When the graft was reimplanted 90° rotated it was predicted that the recovered projection would show a corresponding 90° rotation over the grafted area. Results tended to show the predicted distortion in the projection though not at the edges of the grafts.It was difficult to draw any useful conclusions from the retinotectal projection of 180° rotated tectum.In another series when the posterior half of the tectum was removed and the entire optic nerve allowed to regenerate, the resulting projection was compressed into the remaining half tectum.There was a gross abnormality in the histological structure of the grafted tectum even in those cases where the restoration of the visual map was more or less normal.An attempt has been made using various microscopic techniques to compare regeneration within tectal grafts with normal tectal development

Kaderi bir çoban tarafından tayin edilen savaş: İkâb Hezimeti (1212)

Müslümanların yaklaşık sekiz asırlık Endülüs serüveni, yaygın olarak kabul edilen görüşe göre 711 yılında İslam ordularının, Târık b. Ziyâd önderliğinde bölgeye girmesi ile başlamıştır. Endülüs’te Müslümanların yaşadığı siyasi süreci; Fetih Dönemi (711-714), Valiler Dönemi (714-756)4, Endülüs Emevîleri Dönemi (756-1031), Mülûküt-Tavâif Dönemi (1031- 1090), Murâbıtlar Dönemi (1090-1147), Muvahhidler Dönemi (1147-1238), Gırnata Emîrliği Dönemi/Nasrîler Dönemi (1238-1492)5 gibi dönemler altında incelemek mümkündür. Endülüs, belirtilen dönemler içerisinde ilim, sanat ve kültür alanında tarihinin altın çağını yaşamakla birlikte aynı zamanda sayısız siyasi mücadelelere de ev sahipliği yapmıştır

Snow Covered with Dust after Chamoli Rockslide: Inference Based on High-Resolution Satellite Data

The high-resolution multi-temporal PlanetScope image of 7 February 2021 clearly shows the fall of a large part of the Nanda Ghunti glacier (Uttarakhand) down in the base of the valley from a height of about 2000 m. The recorded seismic signals at the local seismic networks, close to the Joshimath station, show the occurrence of the fall of the first glacier block followed by another block which corresponds to the seismic signal recorded the second time. The timings of signals recorded from the seismic station are related to the visual sign of local dust in the valley after the fall of the glacier blocks at 05:01 AM and 05:28 AM UTC on 7 February 2021. In the present paper, we carried out the changes in spectral signatures of PlanetScope imageries and backscattering coefficients from Sentinel-1 synthetic aperture radar (SAR) data at six different locations. Our analysis suggests pronounced changes at all locations based on spectral signatures and backscattering coefficients due to deposition of snow dust due to the fall of the glacier blocks. Changes in surface wetness are evident after the melting of snow due to the deposition of dust in the valley

Changes in the Flood Plains and Water Quality Along the Himalayan Rivers After the Chamoli Disaster of 7 February 2021

The Himalayan regions are vulnerable to all kinds of natural hazards. On 7 February 2021, a deadly disaster occurred near the Tapovan, in Uttarakhand, Himalayas. During the event, large volume of debris along with broken glacial fragments flooded the Rishi Ganga River and washed away the nearby hydropower plants (Rishi Ganga and Tapovan), which was revealed from detailed analysis of multi spectral and bi-temporal satellite data. We present the impact of the Chamoli disaster on the flood plains and water quality of Himalayan rivers, Rishi Ganga near Tapovan, Alaknanda near Srinagar and Ganga near Haridwar and Bijnor. We used four locations along four sections of Himalayan rivers and have analysed various indices, modified normalized difference water index, normalized difference chlorophyll index, and normalized difference turbidity index, to study the changes in water quality and flood plains. On comparison of the spectral and backscattering coefficients derived from Sentinel-2 optical and Sentinel-1 synthetic aperture radar data, changes in the water quality and flood plains of the rivers were found

Chamoli Disaster: Pronounced Changes in Water Quality and Flood Plains Using Sentinel Data

The Himalayan rivers are vulnerable to devastating flooding caused by landslides and outbreak of glacial lakes. On 7 February 2021, a deadly disaster occurred near the Rishi Ganga Hydropower Plant in the Rishi Ganga River, killing more than 100 people. During the event, a large volume of debris and broken glacial fragments flooded the Rishi Ganga River and washed away the Rishi Ganga Hydropower plant ongoing project. This study presents the impact of the Chamoli disaster on the water quality of Rishi Ganga River in upstream near Tapovan and Ganga River in downstream near Haridwar through remote sensing data. Five points have been used at different locations across the two study areas and three different indices were used such as Normalized difference water index (NDWI), Normalized difference turbidity Index (NDTI), and Normalized difference chlorophyll index (NDCI), to analyze changes in water quality. Spectral signatures and backscattering coefficients derived from Sentinel-2 Optical and Sentinel-1 Synthetic-aperture radar (SAR) data were also compared to study the changes in water quality. It was evident from the water quality indices and spectral signatures that the flood plains changed significantly. Using spectral signatures and different indices, the water level in the Chilla dam canal near Haridwar was found to decreased after the Chamoli disaster event as the flood gates were closed to stop the deposit of sediments in the canal. Results suggest changes in water quality parameters (turbidity, chlorophyll concentration, NDWI) at the five locations near the deadly site and far away at Haridwar along the Ganga River. This study is a preliminary qualitative analysis showing changes in river flood plain and water quality after the Chamoli disaster