163 research outputs found
Electron tomography of meiotic spindles in males of the trioecious nematode Auanema rhodensis
The nematode Auanema rhodensis has recently been established as a new model organism. A. rhodensis is characterized by the simultaneous existence of three phenotypical sexes (males, females and hermaphrodites; called trioecy), skewed sex ratios which do not follow Mendel's laws, and variant segregation patterns according to sex and type of gametogenesis. Recently, A. rhodensis has been used to study the possible mechanisms for sex determination in three-sexed species and the variability of basic processes during sexual reproduction including meiotic divisions. During male meiosis, a diploid primary spermatocyte undergoes two consecutive divisions to form four haploid spermatids. Surprisingly, male meiosis in A. rhodensis results in two functional and two nonfunctional spermatids depending on the presence of an X-chromatid. A. rhodensis males exhibit a set of paired autosomes and one single X-chromosome, like males of the wellestablished nematode model organism Caenorhabditis elegans. In contrast to C. elegans, however, the X-chromosome in A. rhodensis divides precociously into its sister chromatids during the first meiotic division followed by a lagging X-chromatid and its uneven distribution during meiosis II. Additionally, the second meiotic divi-sion within this species is characterized by an asymmetric organelle distribution and a spindle structure reminiscent of a monopolar spindle. In this study, serial section electron tomography was used to analyse the ultrastructure of the microtubule skeleton in spermatocytes of A. rhodensis. The analysis of spermiogenesis using electron tomography posed some key advantages compared to standard transmission electron microscopy. First, the microtubule (MT) network could be studied in detail including spindle formation, organization of spindle poles, rearrangement of MTs, and inter-action between MTs and chromosomes. Second, the number and shape of chromosomes could be visualized. And third, the morphology of organelles could be observed at high resolution, and different organelles as well as their distribution pattern could be distinguished and quantified. This study provides highresolution 3D information about male meiosis in A. rhodensis. The results of this thesis confirm the complexity of the male meiotic program and the promi-nent position of the X-chromatid in meiosis II in this organism. Like previous light microscopic studies, electron tomography supports the hypothesis of an X-chromatid-dependent distribution of cellular organelles such as fibrousbody membranousorganelles (FB-MOs) and mitochondria. Furthermore, the formation of an asymmetric spindle could be observed with progressing anaphase II and might be associated with the X-chromatid distribution. Additionally, the analysis of the number of chromosome-associating MTs and their association character gives new insights into possible chromosome segregation mechanisms. Finally, significant differences to the male meiotic program in C. elegans have been identified. For the first time, the MT network in A rhodensis spermatocytes of different division stages has been observed in detail, and several different analyses could be done, including an analysis of the length distribution of MTs in the spindles. Because this ultrastructural analysis is based on fixed samples, live-cell imaging should be performed in the future to gain further information on the chromosome dynamics in this species.Der Fadenwurm Auanema rhodensis hat sich in den letzten Jahren mehr und mehr zu einem neuen Modellorganismus entwickelt. Typisch für A. rhodensis ist das zeitgleiche Vor-kommen dreier phänotypischer Geschlechter (Männchen, Weibchen und Hermaphroditen; die sogenannte Triözie) und deren zahlenmäßig ungleiches Verhältnis zueinander, welches sich nicht durch Mendelsche Regeln erklären lässt. Ebenfalls auffällig sind nach Geschlecht und Gametogenese (Oogenese oder Spermatogenese) abweichende chromosomale Segregationsmuster. Unlängst hat A. rhodensis zu Erkenntnissen über die Geschlechtsdeterminierung in dreigeschlechtlichen Arten und die Varianz grundlegender Prozesse in der Meiose beigetragen. Während der männlichen Meiose (Spermatogenese) teilt sich eine diploide primäre Vorläuferzelle (primäre Spermatozyte) in zwei aufeinanderfolgenden Teilungen in insgesamt vier haploide Spermatiden. Bei A. rhodensis führt die Spermatogenese ungewöhnlicher-weise zu zwei funktionalen und zwei nicht-funktionalen Spermatiden, wobei die Funktionsfähigkeit vom Auftreten eines X-Chromatids abhängt. Männchen von A. rhodensis besitzen, ähnlich wie im Modellorganismus Caenorhabditis elegans, eine Reihe gepaarter Autosomen sowie ein einzelnes X-Chromosom. Im Gegensatz zu C. elegans teilt sich das ungepaarte X-Chromosom in A. rhodensis vorzeitig schon während der ersten meiotischen Teilung in seine Chromatiden, wodurch es zu einer verzögerten und ungleichen Verteilung des X-Chromatids während der zweiten meiotischen Teilung kommt. Diese zweite meiotische Teilung bei A. rhodensis ist außerdem durch eine asymmetrische Verteilung der Organellen und Mikrotubuli gekennzeichnet, letztere ähneln einer monopolaren Spindel. In dieser Arbeit wurde die Methode der seriellen Elektronentomographie genutzt, um die Ultrastruktur der Mikrotubuli in meiotischen Spindeln in Spermatozyten von A. rhodensis zu untersuchen. Zum einen wurden mittels Elektronentomographie das Netzwerk der Mikrotubuli und die Spindelorganisation, die Struktur der Spindelpole sowie die Interaktion zwischen Mikrotubli und Chromosomen drei-dimensional (3D) analysiert. Zum anderen wurde die Form der Chromosomen und die Morphologie und Verteilung der verschiedenen Organellen quantitativ erfasst. Somit stellt diese Studie hochauflösende 3D-Information über den Ablauf der männlichen Meiose in A. rhodensis zur Verfügung und bestätigt damit die Komplexität der männlichen Meiose und die zentrale Rolle des X-Chromatids während der zweiten meiotischen Teilung in diesem Organismus. Basierend auf vorangegangenen lichtmikroskopischen Experimenten an fixierten Proben unterstützt die Elektronentomographie die Hypothese einer vom X-Chromatid abhängigen Verteilung zellulärer Organellen wie spermienspezifischer FB-MOs oder Mitochondrien während der zweiten meiotischen Teilung. Außerdem konnte die Ausbildung einer asymmetrischen Spindel beobachtet werden, welche ebenfalls mit der ungleichen Verteilung des X-Chromatids in Zusammenhang stehen könnte. Eine zusätzliche Analyse chromosomenassoziierter Mikrotubuli brachte erste Erkenntnisse über mögliche zugrundeliegende Mechanismen der Chromosomensegregation. Die Ergebnisse dieser Arbeit konnten mit ähnlichen Untersuchungen in C. elegans verglichen und Unterschiede herausgearbeitet werden.
Zum ersten Mal wurden hier meiotische Spindeln unterschiedlicher Teilungsstadien in 3D untersucht und unterschiedliche quantitative Analysen zur Längenverteilung der Mikrotubuli durchgeführt. Da alle hier gewonnenen Ultrastrukturdaten auf fixierten Proben basieren, sollte eine Betrachtung einer transgenen Wurmlinie mit Fluoreszenzmarkern mittels live-cell imaging auf diese Ultrastrukturanalyse folgen
Provisioning Ultra-Low Latency Services in Softwarized Network for the Tactile Internet
The Internet has made several giant leaps over the years, from a fixed to a mobile Internet, then to the Internet of Things, and now to a Tactile Internet. The Tactile Internet is envisioned to deliver real-time control and physical tactile experiences remotely in addition to conventional audiovisual data to enable immersive human-to-machine interaction and allow skill-set delivery over networks. To realize the Tactile Internet, two key performance requirements, namely ultra-low latency and ultra-high reliability need to be achieved. However, currently deployed networks are far from meeting these stringent requirements and cannot efficiently cope with dynamic service arrivals/departures and the significant growth of traffic demands. To fulfill these requirements, a softwarized network enabled by network function virtualization (NFV) and software-defined network (SDN) technologies is introduced as a new promising concept of a future network due to its flexibility, agility, scalability and cost efficiency. Despite these benefits, provisioning Tactile Internet network services (NSs) in an NFV-based infrastructure remains a challenge, as network resources must be allocated for virtual network function (VNF) deployment and traffic routing in such a way that the stringent requirements are met, and network operator’s objectives are optimized. This problem is also well-known, as NFV resource allocation (NFV-RA) and can be further divided into three stages: (i) VNF composition, (ii) VNF embedding/placement and (iii) VNF scheduling.
This thesis addresses challenges on NFV-RA for Tactile Internet NSs, especially ultra-low latency NSs. We first conduct a survey on architectural and algorithmic solutions proposed so far for the Tactile Internet. Second, we propose a joint VNF composition and embedding algorithm to efficiently determine the number of VNF instances to form a VNF forward graph (VNF-FG) and their embedding locations to serve ultra-low latency NSs, as in some cases, multiple instances of each VNF type with proper embedding may be needed to guarantee the stringent latency requirements. The proposed algorithm relies on a Tabu search method to solve the problem with a reasonable time. Third, we introduce real-time VNF embedding algorithms to efficiently support ultra-low latency NSs that require fast service provisioning. By assuming that a VNF-FG is given, our proposed algorithms aim to minimize the cost while meeting the stringent latency requirement. Finally, we focus on a joint VNF embedding and scheduling problem, assuming that ultra-low latency NSs can arrive in the network any time and have specific service deadlines. Moreover, VNF instances once deployed can be shared by multiple NSs. With these assumptions, we aim to optimally determine whether to schedule NSs on already deployed VNFs or to deploy new VNFs and schedule them on newly deployed VNFs to maximize profits while guaranteeing the stringent service deadlines. Two efficient heuristics are introduced to solve this problem with a feasible time
The Retina in Health and Disease
Vision is the most important sense in higher mammals. The retina is the first step in visual processing and the window to the brain. It is not surprising that problems arising in the retina lead to moderate to severe visual impairments. We offer here a collection of reviews as well as original papers dealing with various aspects of retinal function as well as dysfunction. New approaches in retinal research are described, such as the expression and localization of the endocannabinoid system in the normal retina and the role of cannabinoid receptors that could offer new avenues of research in the development of potential treatments for retinal diseases. Moreover, new insights are offered in advancing knowledge towards the prevention and cure of visual pathologies, mainly AMD, RP, and diabetic retinopathy
Whole-Body Regeneration
This Open Access volume provides a comprehensive overview of the latest tools available to scientists to study the many facets of whole-body regeneration (WBR). The chapters in this book are organized into six parts. Part One provides a historical overview on the study of the WBR phenomena focusing on the primary challenges of this research. Parts Two and Three explore a series of non-vertebrate zoological contexts that provide experimental models for WBR, showing how they can be approached with cellular tools. Parts Four, Five, and Six discuss the future advancements of WBR, reporting about the cutting-edge techniques in genetics and omics used to dissect the underlying mechanisms of WBR, and systems biology approaches to reach a synthetic view of WBR. Written in the highly successful Methods in Molecular Biology series format, chapters include introductions to their respective topics, lists of the necessary materials and reagents, step-by-step, readily reproducible laboratory protocols, and tips on troubleshooting and avoiding known pitfalls. Authoritative and thorough, Whole-Body Regeneration: Methods and Protocols is a valuable resource for scientists and researchers who want to learn more about this important and developing field
A Comprehensive Survey on the Cyber-Security of Smart Grids: Cyber-Attacks, Detection, Countermeasure Techniques, and Future Directions
One of the significant challenges that smart grid networks face is
cyber-security. Several studies have been conducted to highlight those security
challenges. However, the majority of these surveys classify attacks based on
the security requirements, confidentiality, integrity, and availability,
without taking into consideration the accountability requirement. In addition,
some of these surveys focused on the Transmission Control Protocol/Internet
Protocol (TCP/IP) model, which does not differentiate between the application,
session, and presentation and the data link and physical layers of the Open
System Interconnection (OSI) model. In this survey paper, we provide a
classification of attacks based on the OSI model and discuss in more detail the
cyber-attacks that can target the different layers of smart grid networks
communication. We also propose new classifications for the detection and
countermeasure techniques and describe existing techniques under each category.
Finally, we discuss challenges and future research directions
Disruption in the Arts
The volume examines aesthetic disruptions within the various arts in contemporary culture. It assumes that the political potential of art is not solely derived from presenting its audiences with openly political content. Rather, it creates a space of perception and interaction using formal means, thus problematizing the self-evidence of hegemonic structures of communication
Reconfigurable multi-carrier transmitters and their application in next generation optical networks
With the advent of new series of Internet services and applications, future networks will have to go beyond basic Internet connectivity and encompass diverse services including connected sensors, smart devices, vehicles, and homes. Today’s telecommunication systems are static, with pre-provisioned links requiring an expensive and time-consuming reconfiguration process. Hence, future networks need to be flexible and programmable, allowing for resources to be directed, where the demand exists, thus improving network efficiency. A cost-effective solution is to utilise the legacy fibre infrastructure more efficiently, by reducing the size of the guard bands and allowing closer optical carrier spacing, thereby increasing the overall spectral efficiency. However, such a scheme imposes stringent transmitter requirements such as frequency stability, which would not be met with the incumbent laser-array based transmitters. An attractive alternative would be to employ an optical frequency comb (OFC), which generates multiple phase correlated carriers with precise frequency separation. The reconfigurability of such a multi-carrier transmitter would enable tuning of channel spacing, number of carriers and emission wavelengths, according to the dynamic network demands.
This research thesis presents the work carried out, in the physical layer, towards realising reconfigurability of an optical multi-carrier transmitter system. The work focuses on an externally injected gain-switched laser-based OFC (EI-GSL), which is a particular type of multi-carrier source. Apart from the detailed characterisation of GSL OFCs, advances to the state of the art are achieved via comb expansion, investigating new demultiplexing methods and system implementations. Firstly, two novel broadband GS-OFC generation techniques are proposed and experimentally demonstrated. Subsequently, two flexible and compact demultiplexing solutions, based on micro-ring resonators and laser based active demultiplexers are investigated. Finally, the application of a reconfigurable multi-carrier transmitter, employed in access and data centre networks, as well as analog-radio over fibre (A-RoF) distribution systems, is experimentally demonstrated
Advanced Technique and Future Perspective for Next Generation Optical Fiber Communications
Optical fiber communication industry has gained unprecedented opportunities and achieved rapid progress in recent years. However, with the increase of data transmission volume and the enhancement of transmission demand, the optical communication field still needs to be upgraded to better meet the challenges in the future development. Artificial intelligence technology in optical communication and optical network is still in its infancy, but the existing achievements show great application potential. In the future, with the further development of artificial intelligence technology, AI algorithms combining channel characteristics and physical properties will shine in optical communication. This reprint introduces some recent advances in optical fiber communication and optical network, and provides alternative directions for the development of the next generation optical fiber communication technology
Advances in Nanomaterials in Biomedicine
Advances in Nanomaterials in Biomedicine” provided a platform for more than 110 researchers from different countries to present their latest investigations in various fields of nanotechnology, new methods and nanomaterials intended for medical applications. Modern achievements in the field of nanoparticle-based diagnostics, drug delivery and the use of various nanomaterials in the treatment of diseases are presented in 11 original articles. The published reviews provide a comprehensive analysis of the current information on the use of nanomedicine in the treatment and diagnosis of cancer and liver fibrosis, in the field of solid tissue engineering and in drug delivery systems
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