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The analytical expressions for beam wander of collimated and focused beam in oceanic turbulence are derived. Compared with the previously integrating ones, it can be seen that the two results are in agreement with each other exactly for the collimated and focused beam, respectively. Further, the influences of three main oceanic parameters (i.e., the rate of dissipation of mean-squared temperature χT, the rate of dissipation of kinetic energy per unit mass of seawater ɛ and the ratio of temperature to salinity contribution to the refractive index spectrum w ) and the beam radius W0 on beam wander are investigated in the collimated and focused beam cases. The results indicate that the beam wander increases as ɛ decreases, χT increases, salinity-induced predominates and W0 decreases in mentioned above cases. In addition, based on the dimensionless quantity BW, the relation between beam wander and the long-term spot size or turbulence-induced beam spot size is investigated. In particular, to distinguish beam wander among different beam types, the relative beam wander is defined. Based on this definition, the increment of beam wander between focused and collimated beam is larger than that of arbitrary beam type (i.e., 0

In this paper, the new approach of correlation function of the complex phase perturbed by oceanic turbulence is shown. Based on this new approach, the general formula of the two-frequency mutual coherence function (MCF) of ultra-short pulses in oceanic turbulence is derived. Using a temporal moments approach and combining with this new formula for the MCF, the analytical expression for the pulse width is deduced. Besides, the quantity of Rytov variance σ R 2 in oceanic turbulence is obtained, which is widely used as a measure of the strength of turbulence. In particular, the on-axis relative pulse broadening and turbulent effective coefficient of ultra-short pulses (i.e., femtosecond–picosecond regime) propagating through oceanic turbulence are investigated.

We have theoretically and numerically investigated the self-healing peculiarity of Airy beams truncated by different decay factors. The self-healing dynamic processes of truncated Airy beams are different from that of blocked Airy beams. The wing with large truncation of Airy beam can propagate much longer distance than that of small truncated wing. When one of the wings is complete truncated, the Airy beam propagates along a straight line and neither self-bending nor self-reconstruction can be observed. The Poynting vector and energy flow are conducted to gain an insight into the physical mechanism. Keywords: (350.5500) Propagation; (050.1940) Diffraction; (260.1960) Diffraction theory; (260.2110) Electronmagnetic optics.

We present the design and implementation of a Named Data Networking (NDN) based Open Storage System plug-in for XRootD. This is an important step towards integrating NDN, a leading future internet architecture, with the existing data management systems in CMS. This work outlines the first results of data transfer tests using internal as well as external 100 Gbps testbeds, and compares the NDN-based implementation with existing solutions.

Genomics datasets are currently managed by iRODS, the Integrated Rule-Oriented Data System, which is an open source data management software. iRODS provides several services, including indexing, publishing, integrity, storage, and provenance. In this work, we investigate how NDN can seamlessly integrate into iRODS to provide simplified and improved functionality such as name-based data discovery, replication, retrieval, and computation at the edge. We show how to integrate these NDN based mechanisms as well as caching into iRODs. Once completely functional, we aim to study NDN's benefits in a live, production system with real users.

In the last decade, the Internet service model has shifted from sharing resources to distributing content. Certain applications such as large science data, CDNs, VoIP and multimedia applications transfer a significant amount of data over the Internet in a time-constrained manner that requires guaranteed in-network resources. The networking community often achieves this by creating point-to-point guaranteed bandwidth paths. However, the current resource reservation solutions are end-to-end and often initiated by users without the knowledge of the underlying network conditions. As a result, the data flowing through these reserved tunnels are not reusable, and in-network resources are not optimally utilized.On the contrary, Information-Centric Networking architectures such as NDN[16] has several properties that can facilitate resource reservations more intelligently. In this work, we present Strategic Caching And Reservation in ICN (SCARI), a protocol for reserving resources on ICN networks. Similar to RSVP[17] in IP networks, SCARI acts as a signaling mechanism before the actual data transfer. In this work, we focus explicitly on scientific dataflows and not on other types of traffic such as real-time audio/video. We show that SCARI reduces network resource consumption by aggregating reservations and strategically caching content in the network.

NDN (Named Data Networking), a promising next-generation architecture, puts named content in the first place of the network and is resilient to many existing DDoS attacks. However, Interest Flooding Attack (IFA), a typical NDN-specific DDoS attack, has been widely recognized as a serious threat to the development of NDN. The existing countermeasures against IFA mainly aim at the scenario that attackers send spoofed Interests at a fairly high rate and intermediate routers near the attackers can timely detect the attack by themselves. Instead, this work focuses on a more sophisticated scenario that carefully-crafted attackers send Interests at a respectively lower rate at the beginning but gradually speed up to keep the victims’ PIT sizes increasing to eventually deplete the PIT resource for legitimate users. We conduct an insightful experimental study of such sophisticated IFAs on a real-world network topology and our experimental results demonstrate that the statistics of intermediate routers near the attackers change more gradually and slightly in such an attack, which makes it more difficult for an intermediate router near the attackers to detect by itself. Based on the analytical results of this study, we discuss a potential detection and countermeasure mechanism against such a sophisticated IFA in which a central controller monitors the network from a global view.

Current scientific workflows such as Climate Science and High Energy Particle Physics (HEP), routinely generate and use large volumes of observed or simulated data. Users are often geographically dispersed and need to transfer large volumes of data over the network for replication, archiving, or local analysis. Scientific communities have built sophisticated applications and dedicated networks to facilitate such data transfers, and yet, users continue to experience failures, delay, and unpredictable transfer latency. Named Data Networking (NDN) is a new Internet architecture that provides a more flexible and intelligent network layer, suitable for large data transfers. In this work, we use a real scientific data flow to demonstrate NDN's flexibility and versatility that makes it a suitable choice for large-data workflows. We use deadline-based data transfers as our driving example since HEP communities widely use them and discuss several NDN forwarding strategies that can help such flows. In addition to using typical forwarding strategies, we propose, at a high level, a bandwidth reservation protocol for NDN and an on-demand high-speed path creation mechanism. Using these as building blocks, we create a deadline-based data transfer protocol and show how NDN can simplify and improve scientific data distribution. Finally, we use a week-long HEP data log to evaluate our protocol analytically.

Bisphenol A (BPA), a widespread pollutant, is reportedly harmful to humans, animals and plants. However, the effect of BPA on plant pollen tube growth, as well as the mechanism involved, remains unclear. Here, we report that BPA significantly inhibited Picea meyeri pollen germination and tube elongation in a dose-dependent manner. Transmission electron microscopy showed that BPA was detrimental to organelles such as mitochondria and Golgi apparatus. Non-invasive detection revealed that BPA inhibited extracellular Ca 2+ influx and promoted intracellular Ca 2+ efflux at the pollen tube tip, thereby inducing a dissipated Ca 2+ gradient. Fluorescence labeling showed that BPA disorganized actin filaments (AFs), which subsequently led to abnormal vesicle trafficking. Furthermore, BPA reduced the activity of acid phosphatase, a typical exocytosis enzyme. Moreover, Fourier transform infrared (FTIR) analysis and subsequent fluorescence labeling revealed that BPA induced an abnormal deposition of cell wall components, including pectins and callose. Taken together, our results indicate that BPA, a ubiquitous environmental pollutant, disturbs Ca 2+ flux in P. meyeri pollen tubes, thus disrupting AF organization, resulting in abnormal actin-dependent vesicle trafficking and further affecting the deposition of cell wall components. These findings provide new insight into the mechanism of BPA toxicity in pollen tube tip growth.

A conventional adaptive optics system utilizing a beacon light on or near the target for wavefront sensing is often used to compensate the phase aberrations of laser beam propagating through optically inhomogeneous media. However, there is no such a spatially coherent emitter could be used in most cases, one must rely on the reflection or scattering light from an uncooperative extended target itself to probe the atmosphere channel. In this paper, we show that an incoherent target return could be utilized to adaptively focus a collimated laser beam onto a rough target through atmospheric turbulence by simulation. A laser transmitting and receiver system combined with a wavefront sensorless adaptive optics system based on the modified stochastic parallel gradient descent (SPGD) algorithm simulation platform is established. The results show that all the maximum intensities among 1000 simulations increased and a single localized region of high intensity was achieved 78.7%. Additionally, we verified the system performance at different turbulent strength and discuss these limitations.

Named-Data Networking (NDN) is proposed as an approach to evolve the Internet infrastructure from a host- to an information-centric (ICN) approach, which is better suited to the current usage of the Internet. However, the deployment of a global NDN-based Internet is still a long way out of reach. The most likely scenario for a global NDN network will be the one based on NDN 'islands' or domains, where interior forwarding and routing of packets is based on NDN principles. The interconnection of NDN domains involves human configuration to set up IP tunnels, implying an unscalable, tedious and error-prone process resulting in static configuration incapable of reacting to ad-hoc requirements or network changes. Leveraging the flexibility of Software-Defined Networking (SDN) can solve aforementioned problems. Due to its dynamic nature, SDN can automatically recognize an NDN service and instruct switches to set up the configuration for actual service deployment. Such a solution significantly eases the deployment of NDN networks. In this paper, we propose a hybrid solution where we combine Software-Defined Networking, more specifically OpenFlow, and eBPF to perform control plane configuration and data plane programmability respectively, to realize connectivity within and across NDN domains. To do so, we have designed eBPF filters that match on NDN traffic, extended the OpenFlow protocol to configure switch data planes with these match filters and enhanced an OpenFlow switch to act accordingly. Our OpenFlow controller written for Ryu performs routing on NDN names and configures switches correspondingly. Additionally, our controller detects NDN domains and sets up IP tunnels between them. Our evaluation shows that our proof-of-concept on, among others, the SciNet testbed autoconfigures an NDN network, successfully providing end-to-end NDN network functionality across multiple domains.

Key message Gymnosperm pollen grains release ATP to the extracellular matrix which is essential for the initiation of pollen germination and tube growth.

The general analytic expression for the temporal spectrum of atmospheric scintillation under weak turbulence condition is derived. It was employed to study the characteristics of the temporal spectra for horizontal uniform path and whole layer atmospheric non-uniform path. In the non-uniform path, the H-V turbulence model and the Gaussian wind speed model are utilized. It has been found that when the receiver diameter is larger than Fresnel scale (λL)1/2, the temporal spectrum of the plane wave have a power law behavior with a scaling index – 17/3 in high-frequency range. The change of the turbulence strength has little influence on the shape of the temporal spectrum. Based on the characteristics of the temporal spectrum, the aperture-averaging and time-averaging effects on scintillation were analyzed in the frequency domain.

Summary Chronic, uncontrollable stress can lead to various pathologies [ 1 , 2 , 3 , 4 , 5 , 6 ]. Adaptive behaviors, such as reward consumption, control excessive stress responses and promote positive health outcomes [ 3 , 7 , 8 , 9 , 10 ]. Corticotrophin-releasing hormone (CRH) neurons in paraventricular nucleus (PVN) represent a key neural population organizing endocrine, autonomic, and behavioral responses to stress by initiating hormonal cascades along the hypothalamic-pituitary-adrenal (HPA) axis and orchestrating stress-related behaviors through direct projections to limbic and autonomic brain centers [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ]. Although stress and reward have been reported to induce changes of c-Fos and CRH expression in PVN CRH neurons [ 19 , 20 , 21 , 22 , 23 ], it has remained unclear how these neurons respond dynamically to rewarding stimuli to mediate the stress-buffering effects of reward. Using fiber photometry of Ca2+ signals within genetically identified PVN CRH neurons in freely behaving mice [ 24 , 25 , 26 ], we find that PVN CRH neurons are rapidly and strongly inhibited by reward consumption. Reward decreases anxiety-like behavior and stress-hormone surge induced by direct acute activation of PVN CRH neurons or repeated stress challenge. Repeated stress upregulates glutamatergic transmission and induces an N-methyl-D-aspartate receptor (NMDAR)-dependent burst-firing pattern in these neurons, whereas reward consumption rebalances the synaptic homeostasis and abolishes the burst firing. Anatomically, PVN CRH neurons integrate widespread information from both stress- and reward-related brain areas in the forebrain and midbrain, including multiple direct long-range GABAergic afferents. Together, these findings reveal a hypothalamic circuit that organizes adaptive stress response by complementarily integrating reward and stress signals and suggest that intervention in this circuit could provide novel methods to treat stress-related disorders.

We numerically investigated the interior connection dynamics of separated sub-filaments generated by the inner beam of double synchronous and coaxial beams. We demonstrated the critical differences from the case of sequential connection of two filaments generated by two asynchronous pulses. It shows that the background reservoir formed by the co-propagation beams has a secondary function of generation of wave-guide interlayer, resulting in a long continuous plasma channel.

With two sets of experimental instruments, laser transmission was investigated through horizontal atmosphere at 1.06 m under fine and haze-fog events. One set of the instruments is an indirect transmission meter used to measure visibility and the other one is a direct transmission meter used to measure the attenuation of laser power. Results show that the variation of transmittance got from laser power (T p ) and that obtained by visibility (T vis ) are highly correlated. For relative humidity (RH) below 85%, the curve of T vis fits that of T p very well. While the RH is above 85%, the T vis is more likely smaller than T p under fine meteorological condition, but under haze-fog condition T vis is larger than T p on the contrary. For different weather condition, the relation efficient between extinction coefficient and visibility is different. Even for similar visibility, the extinction coefficient of haze-fog event is larger than that of fine event.

The influence of geometrical focusing on the filamentation of femtosecond laser pulses at various low pressures (

A new single-frame blind deconvolution algorithm for the linear shift-invariant imaging system is presented. The algorithm processes the partial images segmented from one single degraded image by multi-frame approach to recover the point spread function (PSF). Then a deconvolution method is employed to restore the whole image with the recovered PSF. In addition, in order to improve the fidelity and resolution of the recovered PSF, the coprimeness of the partial images is utilized. Results of simulated and real atmospheric turbulence degraded images using the algorithm are reported.

A reconstruction method is presented to deal with spatially misaligned and turbulence degraded images that contain shift and rotation motion. This method is implemented through bringing the channels into spatial alignment via image registration and then restoring the original images by a new multiframe blind deconvolution. A frequency domain technique is introduced to precisely register the spatially misaligned images. New priori information of temporal signatures is adopted to constrain the solution in the blind deconvolution. Results show that by the proposed method high quality image can be recovered from spatially misaligned and turbulence degraded images.

We present the numerical simulation and analysis of the bandwidth estimation for adaptive optics (AO) systems based on stochastic parallel gradient descent (SPGD) optimization. Time-varying atmosphere turbulence due to wind velocity and turbulence structure constant is considered in the dynamic simulation. The performance of SPGD system with different iteration frequencies is studied in detail. A formula given that estimates the Strehl ratio degradation after SPGD adaptive control due to the increasing proportion of the number of deformable mirror actuator times Greenwood frequency to iteration frequency based on numerical analyses, can be used to roughly predict the required iteration frequency under the condition of various Greenwood frequencies. OCIS codes: 010.0010, 010.1080, 010.1330. doi: 10.3788/COL201210.S10102. Recently, adaptive optics (AO) systems based on stochastic parallel gradient descent optimization (SPGD) have shown great potential on compensation of phase distortions induced by wave propagation through atmosphere

A blind image deconvolution algorithm in the frequency domain is proposed which uses the edge-preserving method and generic bandwidth of optical system. Generic bandwidth of optical system is analyzed. With the benefits of bandwidth and edge-preserving method as compelling constraints, the algorithm cannot only suppress noise effectively but also restrict the bandwidth of point-spread function (PSF), so high-quality result can be obtained. The new algorithm is superior in handling unregistered channels. The performance of this approach is investigated with simulated data. As shown in our investigation, the algorithm can significantly alleviate the artifacts produced by the deconvolution process.

Many scientific domains, such as climate science and High Energy Physics (HEP), have data management requirements that are not well supported by the IP network architecture. Named Data Networking (NDN) is a new network architecture whose service model is better aligned with the needs of data-oriented applications. NDN provides features such as best-location retrieval, caching, load sharing, and transparent failover that would otherwise be painstakingly (re-)implemented by each application using point-to-point semantics in an IP network. We present the first scientific data management application designed and implemented on top of NDN. We use this application to manage climate and HEP data over a dedicated, high-performance, testbed. Our application has two main components: a UI for dataset discovery queries and a federation of synchronized name catalogs. We show how NDN primitives can be used to implement common data management operations such as publishing, search, efficient retrieval, and publication access control.

The analytical expressions for wave structure function of plane and spherical waves are derived both in the viscous dissipation and inertial range. Due to previously research, there is a discrepancy between theoretical results and the experimental datum in viscous dissipation range. In this paper, only considering the inertial range, taking plane waves for example, we give a comparison of results of WSF calculated by the analytical formula obtained in this paper and the numerical calculations of the definition at the fixed parameter (i.e., the generalized exponent α), it can be seen that the two results are in agreement with each other exactly. Based on non-Kolmogorov power spectrum, new characteristics for wave structure function (WSF) have been found for plane and spherical wave models when the different ratio of inner scale l 0 and outer scale of turbulence L 0 is obtained. In outer scale assumed finite case (i.e., L 0 =1m), WSF obtains the maximum when α approximates to 3.3 both for plane and spherical wave models. In outer scale assumed infinite case (i.e., L 0 = ∞), the WSF can be sorted into three parts, including two rapid-rising regions (i.e., 3.0 0 ) are investigated under mentioned above conditions for two models. In L 0 = 1m case, both for plane and spherical waves, the value of α determines the bump position of WSF. In L 0 = ∞ case, the bump of scaled WSF disappears when the generalized exponent has large values. The changings of scaled WSF monotonically increase as α increased when the generalized exponent is larger than11/3 for two models. Besides, the properties of spherical waves are similar to plane waves, except which the values of WSF and the scaled WSF are smaller than plane ones.

As a distinctive feature of Information Centric Networking (ICN), in-network caching plays a fundamental role on system performance. The line-speed requirement of in-network caching invalidates the employ of complex collaborative caching schemes. The cache management of in-network caching includes three components - cache placement, cache replacement and cache location. Coupling the three pieces would make more efficient use of in-network caches, but existing in-network caching schemes consider only one or two of the three pieces. This work enhances in-network caching with a low complexity cache placement scheme that takes into account content popularity, hop reduction gains, cache space contention and replacement penalty and couples with cache replacement and location, here dubbed PRL (coupling cache Placement, Replacement and Location). PRL keeps data chunks that are more popular and farther away to fetch at an en-route router with less cache space contention. And PRL locates cached copies so as to serve a higher proportion of requests from in-network caches. Our preliminary simulation results suggest that PRL increases cache hit ratio and reduces the average hop count traversed by users' requests and the caching operations at routers as compared to existing representative innetwork caching schemes.

The analytical expression for the root-mean-square (Rms) beam width of the radial Gaussian beam array propagating in oceanic turbulence is derived, where the coherent combination is considered. Meanwhile, the analytical expression for effect of the turbulence on the beam F is also obtained. Giving a comparison of results of F calculated by the analytical expression and the previously integrating one, it can be seen that the two results are in agreement with each other exactly. Further, the influences of the rate of dissipation of mean-squared temperatureχ(T), the rate of dissipation of kinetic energy per unit mass of seawater εand the ratio of temperature to salinity contribution to the refractive index spectrum w are investigated. The results indicate that the Rms beam width increases as χ(T) increases, εdecreases and the salinity-induced turbulence dominates. Moreover, the changings of effective radius of curvature with mentioned above parameters are studied. The strength of turbulence determines the value of effective radius of curvature, and which decreases asχ(T) and w increases, and εdecreases.

The respective contributions of the higher-order Kerr effect (HOKE) and plasma on the propagation of filamentation have been investigated by a modified model, which indicates that HOKE can act as a counterpart of plasma. The determining role of the combination of Kerr self-focusing, defocusing due to HOKE and the plasma generation in the formation of a lengthy filament is confirmed visually. It is favorable to support the view that the general standard Kerr-plasma model should be renewed in some cases accordingly.

The entangled orbital angular momentum (OAM) three photons propagating in Kolmogorov weak turbulence are investigated. Here, the single phase screen model is used to study the entanglement evolution of OAM photons. The results indicate that the entangled OAM three-qubit state with higher OAM modes will be more robust against turbulence. Furthermore, it is found that the entangled OAM three-qubit state has a higher overall transmission for small OAM values.

Recent work has indicated that ghost imaging might find useful application in standoff sensing where atmospheric turbulence is a serious problem. There has been theoretical study of ghost imaging in the presence of turbulence. However, most work has addressed signal-wavelength ghost imaging. Two-wavelength ghost imaging through atmospheric turbulence is theoretically studied in this paper. Based on the extended Huygens-Fresnel integral, the analytical expressions describing atmospheric turbulence effects on the point spread function (PSF) and field of view (FOV) are derived. The computational case is also reported.

Non-classical polarization properties of dark hollow beams propagating through non-Kolmogorov turbulence are studied. The analytic equation for the polarization degree of the quantization partially coherent dark hollow beams is obtained. It is found that the polarization fluctuations of the quantization partially coherent dark hollow beams are dependent on the turbulence factors and beam parameters with the detection photon numbers. Furthermore, an investigation of the changes in the on-axis propagation point and off-axis propagation point shows that the polarization degree of the quantization partially coherent dark hollow beams presents oscillation for a short propagation distance and gradually returns to zero for a sufficiently long distance.

Adaptive optics correcting technique based on stochastic parallel gradient descent (SPGD) control algorithm is an alternative approach which is independent of wavefront sensor and optimizes the performance metric directly. In this paper we establish a simulation model of tip-tilt adaptive optics system, where SPGD optimization algorithm is used to correct the tip-tilt aberration induced by dynamic turbulence. The distance between the measured centroid of a blurring image and the demarcated centroid of the ideal image is considered as the system performance metric, and signals applied to compensation of the drifting atmosphere are generated for tip-tilt mirror. The sensitivity of the performance metrics is investigated, and the convergence rate and the stability are analyzed. By means of this optimization algorithm, the centroid of the image is modified in real time, which results in the improvement of the long exposure image.

Peer-to-Peer(P2P) network has some closer relation-ship with Internet while the scale of P2P network increases. Active P2P worms attack neighbour peers based on hit-list and pose a severe threat to both P2P network and Internet. Due to the complexity of P2P network, the traditional worms propagation model cannot be adequate to exact model P2P worms spread. Both the dynamic characteristic of P2P network and the heterogeneity of peers could have some great impact on active P2P worms spread. A mathematical model of active P2P worms propagation is presented in this paper. We simulate active P2P worms spread after analyzing the mathematical model. The results show that many factors could affect the propagation of active P2P worms such as the state of P2P network, the scan rate of P2P worms, and the security knowledge peers have. We also study the late phase of active P2P worms spread and find that a very small space of P2P network is enough to guarantee active P2P worms self-propagation when peers cannot repair security holes in time for many reasons.

The threats to Internet have been also posed to the social networking sites. In social networks people tend to reduce the original alert and this makes it easier for malware to spread. In this paper we study the threats to social networks in recent years and analyze the targets what the attackers want and the methods how attackers perform the attacks. We separate social networks into two parts: user and social networking site. Then we discuss in details the countermeasures against the threats to social networks. In the end we propose a security framework of social networks.

A deniable authentication allows the receiver to identify the source of the received messages but cannot prove it to any third party. However, the deniability of the content, which is called restricted deniability in this paper, is concerned in electronic voting and some other similar application. At present, most non-interactive deniable authentication protocols cannot resist weaken key-compromise impersonation (W-KCI) attack. To settle this problem, a non-interactive identity-based restricted deniable authentication protocol is proposed. It not only can resist W-KCI attack but also has the properties of communication flexibility. It meets the security requirements such as correctness, restricted deniability as well. Therefore, this protocol can be applied in electronic voting.

Based on the characteristics of a hypergeometric function, the analytical expressions for the phase structure function and angle-of-arrival (AOA) fluctuations of plane and spherical waves propagating through oceanic turbulence are derived. The results are verified by comparing them with the numerical calculations of the definitions using four important parameters (i.e., the rate of dissipation of mean-squared temperature the rate of dissipation of kinetic energy per unit mass of fluid the ratio of temperature to salinity contribution to the refractive index spectrum and the Kolmogorov microscale The relation between AOA fluctuations and the spatial coherence radius is also investigated.

By investigating the spatial and temporal variations of the propagating pulses, we have shown for the first time that the lattice waveguides can induce nonlinear effects to tailor the plasma channel generated by a femtosecond laser pulse. Different types of the spatiotemporal localized nonlinear light bullet’s propagating configurations have been predicted. By adjusting the parameters of the modulation potential, longer continuum filaments and reshaped laser pulses can be obtained, due to the focusing nonlinearity of the lattice modulation index.

The Euro50 is an extremely large telescope for optical and infrared wavelength with a 50 m primary mirror. It has a segmented, aspherical primary mirror and an aspherical, deformable secondary in a Gregorian layout. A tentative conceptual design exists and has been documented in a study report. Recent activities have concentrated on the science case for extremely large telescopes in the 50 m class and on identification of potential technical "show stoppers". The science case investigation has identified four fields of particular interest. The studies of critical technical issues have concentrated on atmospheric dispersion effects for high-resolution adaptive optics for extremely large telescopes, and on the influence of wind and other disturbances on wavefront control. Wind load on the telescope, the primary mirror and the enclosure has been studied using wind tunnel measurements and computational fluid dynamics. The impact of wind on the total system has been investigated using an integrated model that includes the telescope structure, the primary mirror segment alignment system, the secondary mirror alignment system, and single conjugate adaptive optics using the deformable secondary mirror. The first, tentative results show that wind disturbances may be significant and that the task of correcting for wind residuals may be at least as large for the adaptive optics system as that of correcting for atmospheric aberrations. The results suggest that use of extremely large telescopes for observations of earth-like planets around nearby stars may imply a considerable challenge (Less)

The Euro50 is an astronomical extremely large telescope for optical and infrared wavelength with a 50 m primary mirror. The telescope will have an elaborate control system ("live optics") to correct for atmospheric and telescope aberrations. To study and predict performance of the complete telescope system, an integrated model combining the structural model of the telescope, optics models, the control systems, and the adaptive optics has been established. Wind is taken into account on the basis of wind tunnel measurements and computer fluid dynamics calculations. Atmospheric aberrations are included using a seven-layer atmosphere model. The integrated model is written in Matlab and is run on a cluster computer to achieve acceptable execution times. Dedicated ordinary differential equation solvers have been written and a special toolkit for communication between Matlab processes on different nodes of the cluster computer has been set up. Preliminary results from the complete integrated model, including adaptive optics, are shown (Less)

Recent studies on laser beam propagating over a long distance through even weak atmospheric turbulence have shown that under conditions where scintillation is significant a continuous phase function does not in general exist, owing to the presence of branch points in the complex optical field. The scintillation can create problems when one is using an adaptive-optics system for atmospheric-turbulence compensation. Significant degradation was observed in the adaptive-optics correction through the results of our simulated experiments with a wave-optics code as the scintillation increased when the Fried parameter r0 remained a constant. As result of the measured gradient field (i.e., idealized pointwise phase differences measurements) including two components, one that is expressed as the gradient of a scalar potential and the other that is expressed as the curl of a vector potential, the scalar and vector potentials are both easily reconstructed from the measured gradients. The total potential (including the scalar and vector potentials) and the scalar potential serve as an upper bound on the performance of Hartmann-sensor reconstruction and Hartmann-sensor-based least-squares reconstruction, respectively. The results obtained illustrate that scintillation effects are not significant until the Rytov number is greater than 0.2. When the Rytov number is greater than 0.2, the performance of adaptive-optics correction is obviously degraded. These computational results showed that the compensative effect of adaptive optics is not characterized completely by Fried parameter. The effect of scintillation needs to be considered in compensation of adaptive optics when a laser beam propagated over a long distance through even weak atmospheric turbulence.