Cloud Members Research Articles

Toward Information-Centric Vehicular Cloud: Technologies, Challenges, and Opportunities

At present, road-safety problems such as traffic accidents have become increasingly serious. In the next ten years, road safety problems will lead to 13 million deaths if no effective measures are taken. Rapid retrieval of road information can prevent most traffic accidents, so it is becoming an important measure to solve road-safety problems. However, with increasing complexity and diversification of road information, an individual vehicle can no longer produce the entire traffic and road information due to limitations of visual angles and resources. In this circumstance, the concept of Vehicular Cloud (VC) is proposed to enable resource sharing and collaboration among cloud members as a solution for overcoming resource limitations. In this article, we analyze the features of VC and the advantages of the information-centric model, and propose that the information-centric model could be an ideal solution for achieving VC. Then, we discuss the open challenges encountered in enabling VC using the information-centric model, and some possible solutions.

The chemical DNA of the Magellanic Clouds

We present the chemical composition of 206 red giant branch stars that are members of the Small Magellanic Cloud (SMC) using optical high-resolution spectra collected with the multi-object spectrograph FLAMES-GIRAFFE at the ESO Very Large Telescope. This sample includes stars in three fields that are located in different positions within the parent galaxy. We analysed the main groups of elements, namely light- (Na), α- (O, Mg, Si, Ca, and Ti), iron-peak (Sc, V, Fe, Ni, and Cu), and s-process elements (Zr, Ba, and La). The metallicity distribution of the sample displays a main peak around [Fe/H]∼–1 dex and a weak metal-poor tail. However, the three fields display different [Fe/H] distributions. In particular, a difference of 0.2 dex is found between the mean metallicities of the two innermost fields. The fraction of metal-poor stars increases significantly (from ∼1 to ∼20%) from the innermost fields to the outermost field, likely reflecting an age gradient in the SMC. We also found an indication of possible chemically and kinematic distinct substructures. The ratios of the SMC stars are clearly distinct from those of Milky Way stars, in particular, for the elements produced by massive stars (e.g. Na, α, and most iron-peak elements), whose abundance ratios are systematically lower than those measured in our Galaxy. This shows that massive stars contributed less to the chemical enrichment of the SMC than the Milky Way, according to the low star formation rate expected for this galaxy. Finally, we identified small systematic differences in the abundances of some elements (Na, Ti, V, and Zr) in the two innermost fields, suggesting that the chemical enrichment history in the SMC has not been uniform.

A Novel Survey for Young Substellar Objects with the W-band Filter. V. IC 348 and Barnard 5 in the Perseus Cloud

We report the discovery of substellar objects in the young star cluster IC 348 and the neighboring Barnard 5 dark cloud, both at the eastern end of the Perseus star-forming complex. The substellar candidates are selected using narrowband imaging, i.e., on and off photometric technique with a filter centered around the water absorption feature at 1.45 μm, a technique proven to be efficient in detecting water-bearing substellar objects. Our spectroscopic observations confirm three brown dwarfs in IC 348. In addition, the source WBIS 03492858+3258064, reported in this work, is the first confirmed brown dwarf discovered toward Barnard 5. Together with the young stellar population selected via near- and mid-infrared colors using the Two Micron All Sky Survey and the Wide-field Infrared Survey Explorer, we diagnose the relation between stellar versus substellar objects with the associated molecular clouds. Analyzed by Gaia EDR3 parallaxes and kinematics of the cloud members across the Perseus region, we propose the star formation scenario of the complex under influence of the nearby OB association.

RSU-Aided Optimal Member Replacement Scheme with Improved Mobility Prediction for Vehicular Clouds in VANETs

The technique of vehicular clouds is considered an attractive approach in VANETs, because it provides a requester vehicle the ability to use resources of neighborhood vehicles (called cloud member vehicles) to construct a vehicular cloud to use next-generation vehicular applications during driving. Generally, member vehicles can move along different routes from the route of the requester vehicle in intersections and, as a result, leave the vehicular cloud. Then, the leaving member vehicle should be replaced by new member vehicles at intersections to reconstruct the vehicular cloud. However, identifying optimal replacement vehicles among many vehicles at intersections is a very difficult task involving minimizing the waste of resources of vehicles due to their irregular mobility. Thus, we propose an optimal member replacement scheme that finds optimal replacement vehicles through the improved mobility prediction of vehicles by borrowing the computational ability of RSUs on intersections. The proposed scheme first makes an improved mobility prediction model by combining both the trajectory prediction of vehicles using the Markov model and the location prediction of vehicles using the Gaussian distribution. Through the improved mobility prediction model, the proposed scheme then determines the leaving member vehicles and calculates their own leaving time. Next, the proposed scheme addresses the problem to find optimal replacement vehicles to minimize the waste resource and solves it through an integer linear programming. For the performance evaluation of the proposed scheme, we implement it in an NS-3 simulator, which includes the Manhattan mobility model, to reflect the mobility of vehicles on roads. Simulation results conducted in various environments verify that the proposed scheme achieves better performance than the existing scheme.

Distributed YSOs in the Perseus Molecular Cloud from the Gaia and LAMOST Surveys

Identifying the young optically visible population in a star-forming region is essential for fully understanding the star formation event. In this paper, we identify 211 candidate members of the Perseus molecular cloud based on Gaia astrometry. We use LAMOST spectra to confirm that 51 of these candidates are new members, bringing the total census of known members to 856. The newly confirmed members are less extincted than previously known members. Two new stellar aggregates are identified in our updated census. With the updated member list, we obtain a statistically significant distance gradient of 4.84 pc deg−1 from west to east. Distances and extinction corrected color–magnitude diagrams indicate that NGC 1333 is significantly younger than IC 348 and the remaining cloud regions. The disk fraction in NGC 1333 is higher than elsewhere, consistent with its youngest age. The star formation scenario in the Perseus molecular cloud is investigated and the bulk motion of the distributed population is consistent with the cloud being swept away by the Per-Tau Shell.

The partial cloud member replacement for reconstructing vehicular clouds in VANETs: Reactive and proactive schemes

Vehicular clouds are considered as an attractive approach because vehicles collaborate using their resources to create value-added services such as safety and entertainment applications. To do this, numerous studies have proposed schemes to construct vehicular clouds among vehicles. However, since vehicles freely move, member vehicles within a vehicular cloud leave the cloud before the end of the cloud service and then the vehicular cloud could be destructed. Thus, a cloud member replacement process is required to substitute the leaving member vehicles with new member vehicles to reconstruct the vehicular cloud. Up to now, the research on cloud member replacement has had little interest and is still in its early stage. Therefore, we propose two partial Cloud Member Replacement(CMR) schemes for reconstructing a vehicular cloud: reactive and proactive. The partial reactive CMR scheme replaces a new member vehicle to reconstruct the vehicular cloud whenever a cloud member leaves and the vehicular cloud is destructed. On the other hand, the partial proactive CMR scheme recognizes all of the leaving member vehicles and replaces them with new member vehicles in advance before the destruction of the vehicular cloud. We first describe the partial reactive and proactive cloud member replacement schemes and next analyze their properties, respectively. Simulation results show that the partial reactive and proactive cloud member replacement schemes achieve better performance than the existing scheme, and they have a tradeoff between them on performance.

Toward Named Data Networking: An Approach Based the Internet of Things Cloud With Edge Assistance

The Internet of Things (IoT) aims to improve the quality of human life by delivering collected data efficiently for real-time monitoring. With the increasing complexity of data, it is hard for an individual IoT device to produce information due to the restrictions of visual angles and resources. For instance, the camera mounted on the front of a vehicle captures only data from the road ahead; it cannot collect information from the side. The local cloud (LC) is a new communication paradigm where cloud members collaboratively generate data locally by sharing their resources, so integration of the IoT and LC (ITLC) should be an effective way to overcome the resource restriction of an individual device. Named data networking (NDN) is a novel and efficient communication mechanism, and its features are able to assist in realizing the ITLC and enhancing the efficiency of ITLC-based data delivery. However, NDN has different architectures and features than the ITLC, so it is challenging to exploit NDN to realize ITLC. In this article, we propose an edge-assisted, NDN-based ITLC framework and provide evaluation results that verify its advances.

Unveiling the Kondo cloud: Unitary renormalization-group study of the Kondo model

We analyze the single-channel Kondo model using the recently developed unitary renormalization-group (URG) method and obtain a comprehensive understanding of the Kondo screening cloud. The fixed-point low-energy Hamiltonian enables the computation of a plethora of thermodynamic quantities (specific heat, susceptibility, Wilson ratio, etc.) as well as spectral functions, all of which are found to be in good agreement with known results. By integrating out the impurity, we obtain an effective Hamiltonian for the excitations of the electrons comprising the Kondo cloud. This is found to contain both $k$-space number diagonal (Fermi liquid) and off-diagonal four-fermion scattering terms. Our conclusions are reinforced by a URG study of the two-particle entanglement and many-body correlations among members of the Kondo cloud and impurity. The entanglement between the impurity and a cloud electron, as well as between any two cloud electrons, is found to increase under flow towards the singlet ground state at the strong-coupling fixed point. Both the number diagonal and off-diagonal correlations within the conduction cloud are also found to increase as the impurity is screened under the flow, and the latter are found to be responsible for the macroscopic entanglement of the Kondo-singlet ground state. The URG flow enables an analytic computation of the phase shifts suffered by the conduction electrons at the strong-coupling fixed point. This reveals an orthogonality catastrophe between the local-moment and strong-coupling ground states and is related to a change in the Luttinger volume of the conduction bath under the crossover to strong coupling. Our results offer fresh insight into the nature of the emergent many-particle entanglement within the Kondo cloud and pave the way for further investigations in more exotic contexts such as the fixed point of the overscreened multichannel Kondo problem.

Massive heartbeat stars from TESS

Context. Heartbeat stars are eccentric binaries that exhibit a characteristic shape of brightness changes close to the periastron passage, primarily caused by a variable tidal distortion of the components. Variable tidal potential can drive tidally excited oscillations (TEOs), which are usually gravity modes. Studies of heartbeat stars and TEOs open up new possibilities for probing the interiors of massive stars. There are only a few massive (masses of components ≳2 M⊙) systems of this type that are known thus far. Aims. Using TESS data from the first 16 sectors, we searched for new massive heartbeat stars and TEOs using a sample of over 300 eccentric spectroscopic binaries. Methods. We analysed 2 min and 30 min cadence TESS data. Then we fitted Kumar’s analytical model to the light curves of stars showing heartbeats and performed a times-series analysis of the residuals searching for TEOs and periodic intrinsic variability. Results. We found 20 massive heartbeat systems, of which 7 exhibit TEOs. The TEOs occur at harmonics of orbital frequencies in the range between 3 and 36, with the median value equal to 9, which is lower than those in known Kepler systems with TEOs. The most massive system in this sample is the quadruple star HD 5980, a member of the Small Magellanic Cloud. With a total mass of ∼150 M⊙ it is the most massive system showing a heartbeat. Six stars in the sample of the new heartbeat stars are eclipsing. A comparison of the parameters derived from fitting Kumar’s model and from light-curve modelling shows that Kumar’s model does not provide reliable parameters. In other words, the orbital parameters can be reliably derived from fitting heartbeat light curves only if the model includes all proximity effects. Finally, intrinsic pulsations of β Cep, SPB, δ Sct, and γ Dor-type were found in nine heartbeat systems. This opens an interesting possibility for studies of pulsation-binarity interaction and the co-existence of forced and self-excited oscillations.

Optimized Bit Matrix based Power Aware Load Distribution Policy for Federated Cloud

Federated Cloud is a next generation cloud computing model which works towards a new dynamic scenario in smart ecosystems. It consolidates individual clouds together to form single large cloud to satisfy all on-demand requirements of the users. Federated cloud is currently facing many challenges including: monitoring of individual cloud services, maintaining service level agreement, fair load distribution, power usage etc. Hence, to address these challenges this paper presents a brokerage model “Optimized Bit Matrix based Power Aware Load Distribution Policy for Federated Cloud (OBMPLP)”. Presented model includes two novel concepts: Bit Matrix and Load Distribution Factor. Bit Matrix constructed by individual cloud members representing resource availability status and environment in executing the user’s request. Load Distribution Factor representing load distribution level at individual cloud. OBMPLP policy dispenses the incoming requests among multiple clouds by analyzing bits pattern and load distribution factor that not only performs fair load distribution among multiple clouds, but also improves response time, alleviate power consumption at each cloud and achieve better quality service. The performance of the proposed policy is evaluated and results demonstrate reduction in response time, optimized power consumption and fair distribution of load compared to existing approaches.

Content Delivery Based on Vehicular Cloud

Nowadays, Vehicular Ad Hoc NETworks (VANETs) become actually the main force to disseminate and deliver position-related contents such as road-safety information, so it is significant to improve content delivery efficiency. Usually, users employ the address-centric mechanism to upload/download contents to/from servers located in backbone networks, which leads to considerable content delivery latency and costs. This paper proposes a Content Delivery solution based on Vehicular Cloud (CDVC) and aims to take advantage of the vehicular cloud and name-based mechanism to reduce the content delivery cost and latency. In CDVC, vehicular cloud members store and provide the content locally so that vehicles can rapidly retrieve the content from the nearest member. Moreover, the hierarchical name-based mechanism is proposed to achieve the request aggregation so that vehicles can share the content via one content delivery process. Finally, CDVC is evaluated, and the experimental data show that CDVC effectively reduces the content delivery cost and latency.

Comet C/2018 V1 (Machholz–Fujikawa–Iwamoto): dislodged from the Oort Cloud or coming from interstellar space?

ABSTRACT The chance discovery of the first interstellar minor body, 1I/2017 U1 (‘Oumuamua), indicates that we may have been visited by such objects in the past and that these events may repeat in the future. Unfortunately, minor bodies following nearly parabolic or hyperbolic paths tend to receive little attention: over 3/4 of those known have data-arcs shorter than 30 d and, consistently, rather uncertain orbit determinations. This fact suggests that we may have observed interstellar interlopers in the past, but failed to recognize them as such due to insufficient data. Early identification of promising candidates by using N-body simulations may help in improving this situation, triggering follow-up observations before they leave the Solar system. Here, we use this technique to investigate the pre- and post-perihelion dynamical evolution of the slightly hyperbolic comet C/2018 V1 (Machholz–Fujikawa–Iwamoto) to understand its origin and relevance within the context of known parabolic and hyperbolic minor bodies. Based on the available data, our calculations suggest that although C/2018 V1 may be a former member of the Oort Cloud, an origin beyond the Solar system cannot be excluded. If extrasolar, it might have entered the Solar system from interstellar space at low relative velocity with respect to the Sun. The practical feasibility of this alternative scenario has been assessed within the kinematic context of the stellar neighbourhood of the Sun, using data from Gaia second data release, and two robust solar sibling candidates have been identified. Our results suggest that comets coming from interstellar space at low heliocentric velocities may not be rare.

Spectroscopic and dynamical properties of comet C/2018 F4, likely a true average former member of the Oort cloud

Context. The population of comets hosted by the Oort cloud is heterogeneous. Most studies in this area have focused on highly active objects, those with small perihelion distances or examples of objects with peculiar physical properties and/or unusual chemical compositions. This may have produced a biased sample of Oort cloud comets in which the most common objects may be rare, particularly those with perihelia well beyond the orbit of the Earth. Within this context, the known Oort cloud comets may not be representative of the full sample meaning that our current knowledge of the appearance of the average Oort cloud comet may not be accurate. Comet C/2018 F4 (PANSTARRS) is an object of interest in this regard. Aims. Here, we study the spectral properties in the visible region and the cometary activity of C/2018 F4, and we also explore its orbital evolution with the aim of understanding its origin within the context of known minor bodies moving along nearly parabolic or hyperbolic paths. Methods. We present observations obtained with the 10.4 m Gran Telescopio Canarias (GTC) that we use to derive the spectral class and visible slope of C/2018 F4 as well as to characterise its level of cometary activity. Direct N-body simulations are carried out to explore its orbital evolution. Results. The absolute magnitude of C/2018 F4 is Hr > 13.62 ± 0.04 which puts a strong limit on its diameter, D < 10.4 km, assuming a pV = 0.04 cometary-like value of the albedo. The object presents a conspicuous coma, with a level of activity comparable to those of other comets observed at similar heliocentric distances. Comet C/2018 F4 has a visible spectrum consistent with that of an X-type asteroid, and has a spectral slope S′ = 4.0 ± 1.0%/1000 Å and no evidence of hydration. The spectrum matches those of well-studied primitive asteroids and comets. The analysis of its dynamical evolution prior to discovery suggests that C/2018 F4 is not of extrasolar origin. Conclusions. Although the present-day heliocentric orbit of C/2018 F4 is slightly hyperbolic, both its observational properties and past orbital evolution are consistent with those of a typical dynamically old comet with an origin in the Oort cloud.

In-situ Star Formation in the Outskirts of the Large Magellanic Cloud: Gaia DR2 Confirmation.

We explore the Gaia data release 2 (DR2) proper motions of six young, main-sequence stars, members of the Large Magellanic Cloud (LMC) reported by Moni Bidin et al. These stars are located in the outskirts of the disk, between 7° and 13° from the LMC's center where there is very low H I content. Gaia DR2 proper motions confirm that four stars formed locally, in situ, while two are consistent with being expelled via dynamical interactions from inner, more gas-rich regions of the LMC. This finding establishes that recent star formation occurred in the periphery of the LMC, where thus far only old populations were known.

Review on dynamic group data sharing in cloud environment

Information sharing or exchange of data within entities plays a significant role in cloud storage. In cloud computing, a robust and practical methodology is developed which can be utilized by cloud users for sharing information among multiple group members in the cloud with lowered maintenance and management costs. Furthermore, a service provider in the cloud does not share data with anyone other than the Trusted Third Party (TTP) sources due to the semi-trusted characteristics of the cloud. In this way, there is no global security mechanism for dynamic group data sharing over the cloud. Subsequently, the Cloud Service Providers (CSPs) can convey different services to cloud users through powerful data centres. Hence, data is secured through the validation of users in the cloud. Meanwhile, CSPs should offer outsourced security assurance for data file sharing. Assuring privacy in data sharing is still a critical issue due to continuous change in cloud users, particularly, for unauthenticated or third party users because of the risk of collusion attacks. However, security concerns turn into a major restraint as outsourcing storage data is perhaps a delicate concern for cloud providers. Additionally, sharing information in a multi-proprietary approach while protecting information and individual security to the data from unauthorized or third party users is still a challenging task as there is a frequent change in cloud members. In this regard, previous studies are reviewed and discussed which are related to dynamic group data sharing using cloud computing.

Where the Solar system meets the solar neighbourhood: patterns in the distribution of radiants of observed hyperbolic minor bodies

Abstract Observed hyperbolic minor bodies might have an interstellar origin, but they can be natives of the Solar system as well. Fly-bys with the known planets or the Sun may result in the hyperbolic ejection of an originally bound minor body; in addition, members of the Oort cloud could be forced to follow inbound hyperbolic paths as a result of secular perturbations induced by the Galactic disc or, less frequently, due to impulsive interactions with passing stars. These four processes must leave distinctive signatures in the distribution of radiants of observed hyperbolic objects, both in terms of coordinates and velocity. Here, we perform a systematic numerical exploration of the past orbital evolution of known hyperbolic minor bodies using a full N-body approach and statistical analyses to study their radiants. Our results confirm the theoretical expectations that strong anisotropies are present in the data. We also identify a statistically significant overdensity of high-speed radiants towards the constellation of Gemini that could be due to the closest and most recent known fly-by of a star to the Solar system, that of the so-called Scholz's star. In addition to and besides 1I/2017 U1 (‘Oumuamua), we single out eight candidate interstellar comets based on their radiants’ velocities.

A Novel Solution for Manufacturing Interoperability Fulfillment using Interoperability Service Providers

The cloud manufacturing paradigm has been known as one of the best solutions for today's competitive manufacturing environments. This paradigm insists on using a manufacturing service oriented approach for fulfilling the manufacturing enterprise resource management by the access to global availability of manufacturing services. The proposed service oriented approach covers a wide area of manufacturing resource management from infrastructures to platforms and applications. However, due to wide global distributions of manufacturing clouds, the service oriented architectures which are designed in the clouds cannot communicate with each other. This is mainly due to concentration of cloud manufacturing paradigm to the application of the detailed manufacturing resource acquisitions through a services oriented approach. To solve this problem a wide area of researches have been established which can be named as the interoperability of manufacturing clouds. In this paper, a novel solution for enabling the interoperability among the manufacturing clouds has been proposed. This solution applies the service oriented approach of the cloud manufacturing to enable the interoperability services. These services are proposed by Information Technology related service provider companies. These firms can provide the different manufacturing clouds with the interoperability services. These services are acquired by the manufacturing cloud members to communicate with other cloud members. The proposed solution enables two important mechanisms. The first mechanism uses service integration functions for enabling an integrated service data model and the second mechanism uses service mapping functions. Finally, the paper has elaborated the architecture of the platform and outlined future works.

THE HAWAII INFRARED PARALLAX PROGRAM. II. YOUNG ULTRACOOL FIELD DWARFS* †

ABSTRACT We present a large, uniform analysis of young (≈10–150 Myr) ultracool dwarfs, based on new high-precision infrared (IR) parallaxes for 68 objects. We find that low-gravity (vl-g) late-M and L dwarfs form a continuous sequence in IR color–magnitude diagrams, separate from the field population and from current theoretical models. These vl-g objects also appear distinct from young substellar (brown dwarf and exoplanet) companions, suggesting that the two populations may have a different range of physical properties. In contrast, at the L/T transition, young, old, and spectrally peculiar objects all span a relatively narrow range in near-IR absolute magnitudes. At a given spectral type, the IR absolute magnitudes of young objects can be offset from ordinary field dwarfs, with the largest offsets occurring in the Y and J bands for late-M dwarfs (brighter than the field) and mid-/late-L dwarfs (fainter than the field). Overall, low-gravity (vl-g) objects have the most uniform photometric behavior, while intermediate gravity (int-g) objects are more diverse, suggesting a third governing parameter beyond spectral type and gravity class. We examine the moving group membership for all young ultracool dwarfs with parallaxes, changing the status of 23 objects (including 8 previously identified planetary-mass candidates) and fortifying the status of another 28 objects. We use our resulting age-calibrated sample to establish empirical young isochrones and show a declining frequency of vl-g objects relative to int-g objects with increasing age. Notable individual objects in our sample include high-velocity (≳100 km s−1) int-g objects, very red late-L dwarfs with high surface gravities, candidate disk-bearing members of the MBM20 cloud and β Pic moving group, and very young distant interlopers. Finally, we provide a comprehensive summary of the absolute magnitudes and spectral classifications of young ultracool dwarfs, using a combined sample of 102 objects found in the field and as substellar companions to young stars.

First stars of theρOphiuchi dark cloud

Star formation in molecular clouds can be triggered by the dynamical action of winds from massive stars. Furthermore, X-ray and UV fluxes from massive stars can influence the life time of surrounding circumstellar disks. We present the results of a 53 ks XMM-Newton observation centered on the Rho Ophiuchi A+B binary system. Rho Ophiiuchi lies in the center of a ring of dust, likely formed by the action of its winds. This region is different from the dense core of the cloud (L1688 Core F) where star formation is at work. X-rays are detected from Rho Ophiuchi as well as a group of surrounding X-ray sources. We detected 89 X-ray sources, 47 of them have at least one counterpart in 2MASS + All-WISE catalogs. Based on IR and X-ray properties, we can distinguish between young stellar objects (YSOs) belonging to the cloud and background objects. Among the cloud members, we detect 3 debris disk objects and 22 disk-less / Class III young stars. We show that these stars have ages in $5-10$ Myr, and are significantly older than the YSOs in L1688. We speculate that they are the result of an early burst of star formation in the cloud. An X-ray energy of $\ge5\times10^{44}$ ergs has been injected into the surrounding medium during the past $5$ Myr, we discuss the effects of such energy budget in relation to the cloud properties and dynamics.

Review On Secure Anti-Collusion Data Sharing For Dynamic Group In The Cloud

Benefited from cloud computing, users can achieve an effective and economical approach for data sharing among group members in the cloud with the characters of low maintenance and little management cost. In multiuser cloud computing there may be a major problem to securely share documents. Frequent change of membership, challenging issues to prevent the system from collusion attack, to secure the system from the revoked user. In this paper we propose a secure data forwarding mechanism for dynamic member. Firstly, we propose a cloud system in which no of server should be present any user must store the file in any server. Secondly, the file must upload in no of blocks in the same server. Thirdly, the data forwarding; the uploading user may forward the data to the requested user in the cloud. If the member of cloud should exchange the information to one another they forward the data to the id of the members. Other member can’t access file in the cloud without permission of file up loader. By this scheme the revoked user can’t access the original data. in this scheme all the time the cloud member get permission from the up loader member for access the information at the time of file transfer up loader know the requested id he provide the server id and no of block to the downloader. The file should store in the server in maximum four no of block i.e. file is splitting in four parts. Each two block should be encrypted and store in the server. RSA and MD-5 encryption algorithm should be used for encrypting four blocks. In multiuser environment user doesn’t know which encryption will used for which block.