Solar Energy Engineering: Processes and Systems

Errata pdf inserted.Η βιβλιοθήκη διαθέτει αντίτυπο του βιβλίου σε έντυπη μορφή με ταξινομικό αριθμό: TJ810 .K35 2009With the threat of global warming, and the gradual depletion of petroleum supplies, solar electric power is rapidly becoming significant part of our energy mix. The range of solar cells spans different materials and different structures in the quest to extract maximum power from the device while keeping the cost to a minimum. Devices with efficiency exceeding 30% have been demonstrated in the laboratory. Solar Energy Engineering: Processes and Systems. Solar Energy Processes and Systems includes all areas of solar energy engineering. All subjects are presented from the fundamental level to the highest level of current research. The book includes subjects such as energy related environmental problems, solar collectors, solar water heating, solar space heating and cooling, industrial process heat, solar desalination, photovoltaics, solar thermal power systems and modelling of solar systems including the use of artificial intelligence systems in solar energy systems modelling and performance prediction

Knowledge and Practices of Cypriot Bovine Farmers towards Effective and Safe Manure Management

Manure from bovine farms is commonly used as an organic fertiliser. However, if not properly managed, it can spread significant biological and chemical hazards, threatening both human and animal health. The effectiveness of risk control hugely relies on farmers' knowledge regarding safe manure management and on the application of suitable management practices. This study aims to evaluate the knowledge and practices of Cypriot bovine farmers towards safer manure management, from its generation to its final use, in line with the One Health approach. Factors affecting farmers' knowledge and applied practices are also investigated through a questionnaire survey. The questionnaire was developed and sent to all eligible bovine farmers in Cyprus (n = 353), and 30% (n = 105) of them returned the completed questionnaire. Results revealed there are some gaps in farmers' knowledge. The use of manure for fertilising crops dominated. Only half of the farmers stored manure in appropriate facilities, with 28.5% of them using a dedicated area with cement floors and 21.5% utilising leakproof tanks. The majority (65.7%) stored manure for more than three months before its use as a fertiliser in a dried form. In multiple regression analysis, education level and farming purpose were significant determinants of farmer knowledge. In conclusion, Cypriot farmers' knowledge must be reinforced to ensure proper manure management. The results highlight the importance of providing relevant training to farmers. Although the current practices partially decrease manure pathogens, interventions to promote the use of more effective treatment methods, such as biogas transformation and composting, would be beneficial

Android at risk: current threats stemming from unprotected local and external resources

Android is an open source platform derived from Linux OS. It utilizes a plethora of resources both local and external. Most of its local resources (e.g procfs nodes) were inherited from Linux with some of them being even- tually removed, while new ones were added to meet the requirements of a mobile multi-purpose platform. Moreover, such a platform compels the in- troduction of external resources which can be used in tandem with a variety of sensors (e.g Bluetooth and NFC) that the device is equipped with. This thesis demonstrates the subtlety involved in this adaptation which, if not performed correctly, can lead to severe information leaks stemming from un- protected local and external resources. It also presents new defense solutions and mitigation strategies that successfully tackle the found vulnerabilities. In particular, this thesis unearths three new side channels on Android OS. Prior to this work, these side channels were considered to be innocuous but here we illustrate that they can be used maliciously by an adversary to infer a user’s identity, geo-location, disease condition she is interested in, invest- ment information and her driving route. These information leaks, stem from local resources shared among all installed apps on Android: per-app data- usage statistics; ARP (Address Resolution Protocol) information; and speaker status (on or off). While harmless on a different setting, these public local resources can evidently disclose private information on a mobile platform and thus we maintain that they should not be freely available to all third-party apps installed on the system. To this end, we present mitigation strategies which strike a balance between the utility of apps that legitimately need to access such information and the privacy leakage risk involved. Unfortunately the design assumptions made while adapting Linux to cre- ate Android is not the only flaw of the latter. Specifically this work is also concerned with the security and privacy implications of using external to the OS resources. Such resources generate dynamic, hard to mediate channels of communication between the OS and an external source through usually a wireless protocol. We explore such implications in connecting smartphones with external Bluetooth devices. This thesis posits that Android falls short in providing secure Bluetooth connections with external devices; ergo its appli- cation in privacy critical domains is at the very least premature. We present a new threat, defined as external-device mis-bonding or DMB for short. To demonstrate the severity of the threat, we perform realistic attacks on popular medical Bluetooth devices. These attacks delineate how an unau- thorized app can capture private data from Bluetooth external devices and how it can help an adversary spoof those devices and feed erroneous data to legitimate applications. Furthermore, we designed an OS-level defense mechanism dubbed Dabinder, that addresses the system’s shortcomings, by guaranteeing that a Bluetooth connection is established only between a legitimate app and its respective accessory. Nevertheless, Bluetooth is not the only inadequately protected external resource with grave privacy ramifications. We have also studied NFC, Au- dio and SMS as potential channels of communication with alarmingly low confidentiality guarantees. We show with real world attacks, that Android’s permission model is too coarse-grained to safeguard such channels while pre- serving the utility of the apps. To better understand the prevalence of the problem we perform a measurement study on the Android ecosystem and discuss our findings. Finally this work presents SEACAT, a novel defense strategy, enhancing Android with flexible security capabilities. SEACAT is a scalable, effective and efficient solution, built on top of SELinux on Android, that enables the protection of channels used to communicate with external to Android re- sources. It achieves both MAC and DAC protection through straightforward and SELinux-compatible policies as the policy language and structure used, is in accordance with the current policy specifications. The system’s design encompasses mirror caching on both the kernel and the middleware layer which facilitates rapid policy enforcement through appropriate and carefully positioned hooks in the system

Analyzing & designing the security of shared resources on smartphone operating systems

Smartphone penetration surpassed 80% in the US and nears 70% in Western Europe. In fact, smartphones became the de facto devices users leverage to manage personal information and access external data and other connected devices on a daily basis. To support such multi-faceted functionality, smartphones are designed with a multi-process architecture, which enables third-party developers to build smartphone applications which can utilize smartphone internal and external resources to offer creative utility to users. Unfortunately, such third-party programs can exploit security inefficiencies in smartphone operating systems to gain unauthorized access to available resources, compromising the confidentiality of rich, highly sensitive user data. The smartphone ecosystem, is designed such that users can readily install and replace applications on their smartphones. This facilitates users’ efforts in customizing the capabilities of their smartphones tailored to their needs. Statistics report an increasing number of available smartphone applications— in 2017 there were approximately 3.5 million third-party apps on the official application store of the most popular smartphone platform. In addition we expect users to have approximately 95 such applications installed on their smartphones at any given point. However, mobile apps are developed by untrusted sources. On Android—which enjoys 80% of the smartphone OS market share—application developers are identified based on self-sign certificates. Thus there is no good way of holding a developer accountable for a malicious behavior. This creates an issue of multi-tenancy on smartphones where principals from diverse untrusted sources share internal and external smartphone resources. Smartphone OSs rely on traditional operating system process isolation strategies to confine untrusted third-party applications. However this approach is insufficient because incidental seemingly harmless resources can be utilized by untrusted tenants as side-channels to bypass the process boundaries. Smartphones also introduced a permission model to allow their users to govern third-party application access to system resources (such as camera, microphone and location functionality). However, this permission model is both coarse-grained and does not distinguish whether a permission has been declared by a trusted or an untrusted principal. This allows malicious applications to perform privilege escalation attacks on the mobile platform. To make things worse, applications might include third- party libraries, for advertising or common recognition tasks. Such libraries share the process address space with their host apps and as such can inherit all the privileges the host app does. Identifying and mitigating these problems on smartphones is not a trivial process. Manual analysis on its own of all mobile apps is cumbersome and impractical, code analysis techniques suffer from scalability and coverage issues, ad-hoc approaches are impractical and susceptible to mistakes, while sometimes vulnerabilities are well hidden at the interplays between smartphone tenants and resources. In this work I follow an analytical approach to discover major security and privacy issues on smartphone platforms. I utilize the Android OS as a use case, because of its open-source nature but also its popularity. In particular I focus on the multi-tenancy characteristic of smartphones and identify the re- sources each tenant within a process, across processes and across devices can access. I design analytical tools to automate the discovery process, attacks to better understand the adversary models, and introduce design changes to the participating systems to enable robust fine-grained access control of resources. My approach revealed a new understanding of the threats introduced from third-party libraries within an application process; it revealed new capabilities of the mobile application adversary exploiting shared filesystem and permission resources; and shows how a mobile app adversary can exploit shared communication mediums to compromise the confidentiality of the data collected by external devices (e.g. fitness and medical accessories, NFC tags etc.). Moreover, I show how we can eradicate these problems following an architectural design approach to introduce backward-compatible, effective and efficient modifications in operating systems to achieve fine-grained application access to shared resources. My work has let to security changes in the official release of Android by Google