Raman spectroscopy of single-wall boron nitride nanotubes

in Nano Letters (2006), 6(8), 1812-1816

Single-wall boron nitride nanotubes samples synthesized by laser vaporization of a hexagonal BN target under a nitrogen atmosphere are studied by UV and visible Raman spectroscopy. We show that resonant ... [more ▼]

Single-wall boron nitride nanotubes samples synthesized by laser vaporization of a hexagonal BN target under a nitrogen atmosphere are studied by UV and visible Raman spectroscopy. We show that resonant conditions are necessary for investigating phonon modes of BNNTs. Raman excitation in the UV (229 nm) provides preresonant conditions, allowing the identification of the A(1) tangential mode at 1370 cm(-1). This is 5 cm(-1) higher than the E-2g mode in bulk h-BN. Ab initio calculations show that the lower frequency of bulk h-BN with respect to large diameter nanotubes and the single sheet of h-BN is related to a softening of the sp2 bonds in the bulk due to interlayer interaction. [less ▲]

Raman spectroscopy on single- and few-layer graphene

in AIP Conference Proceedings (2007), 893

We report on Raman measurements of single- and few-layer graphene flakes. Raman mapping in combination with scanning force microscopy allows us to locally relate the thickness of the graphite flake with ... [more ▼]

We report on Raman measurements of single- and few-layer graphene flakes. Raman mapping in combination with scanning force microscopy allows us to locally relate the thickness of the graphite flake with the spectral properties. It turns out that the width of the D' line is highly sensitive to the transition from single- to double-layer graphene. The defect-induced D line is found to be most prominent at steps between sections of different height and along the edge of the graphite flake. [less ▲]

Rampini, Asca

in Thill, Jean (Ed.) Luxemburger Musiklexikon (2020)

RAN Resource Slicing Mechanisms for Multiplexing of Multiple Services in 5G Downlink Wireless Networks

Doctoral thesis (2021)

The fifth-generation (5G) of wireless networks majorly supports three categories of services, namely, enhanced mobile broadband (eMBB), ultra-reliable and low latency communications (URLLC), and massive ... [more ▼]

The fifth-generation (5G) of wireless networks majorly supports three categories of services, namely, enhanced mobile broadband (eMBB), ultra-reliable and low latency communications (URLLC), and massive machine-type communications. Every service has its own set of requirements such as higher data rates, lower latency in packet delivery, high reliability, and network energy-efficiency(EE) to support applications including ultra-high definition (UHD) video streaming, virtual reality (VR), autonomous vehicles, vehicular communications, smart farming, and remote-surgery, respectively. The existing one-size-fits-all services network model is not a viable option to support these services with stringent requirements. Therefore, accommodation of these different services on the same physical network while ensuring their distinct QoS requirements is a major challenge. To address this problem, a new concept called network slicing (NS) has emerged as a promising solution for the dynamic allocation of resources to wireless services with different QoS demands. The NS can be formed in both the radio access network (RAN) and core network (CN) parts. In this thesis, we concentrate on RAN resources slicing, and more specifically on challenges that reside in the assignment of limited radio resources to manage the distinct traffic demands occurring from a wide variety of users belonging to heterogeneous services. Specifically, we address the RAN optimization method for joint allocation of time, frequency, and space resources to the eMBB, URLLC, and mMTC users according to their traffic demands (i.e., queue status). Our work in this thesis can be broadly classified into three parts based on the objective function considered in the resource optimization problem: 1) sum-rate maximization, 2) power minimization, 3) EE maximization. In the first part of this thesis, we address an adaptive modulation coding (AMC) based resource allocation problem for dynamic multiplexing of URLLC and eMBB users on the shared resources of the OFDMA-based wireless downlink (DL) network. Specifically, we formulate the resource blocks (RBs) allocation problem as a sum-rate maximization problem subject to the minimum data rate constraint, the latency-related constraint, orthogonality, and reliability constraints. Furthermore, to allocate RBs and transmit power jointly to the users, we also formulate the AMC-based optimization problem to maximize the sum good-put of eMBB users subject to URLLC and eMBB users’ QoS constraints. Importantly, in this problem formulation, we consider a probabilistic constraint to incorporate CSI imperfections and a short-packet communication model for URLLC service. In the second part of this thesis, we formulate the joint RBs and transmit power allocation problem to minimize the transmit power consumption at the BS while guaranteeing the QoS constraints of eMBB, URLLC, and mMTC users and probabilistic constraint to incorporate CSI imperfection, respectively. Importantly, we consider mixed-numerology-based RB grid models to the users according to their queue status/traffic demand for satisfying their stringent requirements. Furthermore, different slicing strategies such as slice-aware (SA) and slice-isolation (SI) resource assignment mechanisms are considered for the efficient co-existence of URLLC, mMTC, and eMBB services on the same RAN infrastructure. The resulting problems in the first and second parts of the thesis are mixed-integer non-linear programming problems (MINLPs) which are intractable to solve. To provide solutions to these problems, we first transform the problems into more tractable using the AMC approximation functions, probabilistic to non-probabilistic conversion functions, Big-M theory, and difference of convex (DC) programming. Later, these transformed problems are solved using the successive convex approximation (SCA) based iterative algorithm. Our simulation results illustrate the performance of our proposed method compared to the baseline methods. Also, the simulation results show the effectiveness of the mixed-numerology-based RB grid model over the fixed numerology grid model and the performance of SA and SI resource slicing strategies in terms of achievable data rates, packet delivery latencies, and queue status, respectively. In the third part of this thesis, different from the first two parts, for the joint assignment of beams, RBs, and transmit power to eMBB and URLLC users, we formulate an EE maximization problem by considering resources scheduling, orthogonality, power-related constraints, and QoS constraints for different services. The resulting mixed-integer non-linear fractional programming problem (MINLFP) is intractable and difficult to solve. To provide a feasible solution, we first transform the formulated problem into a tractable form using fractional programming theory, approximation functions and later utilize the Dinklebach iterative algorithm, DC programming, and SCA to solve it. Finally, we compare the performance of the proposed method against baseline schemes through simulation results. In particular, we show the performance of RAN slicing mechanisms with the mixed and fixed-numerology-based RBs grid models in terms of achievable EE, packet latencies, data rates, total sum-rate, and computational complexity. The proposed algorithm outperforms the baseline schemes in terms of achieving higher data rates for eMBB users. The results also show the trade-off between the total achievable sum rate and EE of the network. The proposed method with mixed numerology grid delivers 20% of higher URLLC packets within 1 ms of latency. Besides, it achieves the lowest computation time than that with the fixed numerology grid. [less ▲]

Random Access based Reliable Uplink Communication and Power Transfer using Dynamic Power Splitting

in IEEE Transactions on Wireless Communications (2020)

Large communication networks, e.g. Internet of Things (IoT), are known to be vulnerable to co-channel interference. One possibility to address this issue is the use of orthogonal multiple access (OMA ... [more ▼]

Large communication networks, e.g. Internet of Things (IoT), are known to be vulnerable to co-channel interference. One possibility to address this issue is the use of orthogonal multiple access (OMA) techniques. However, due to a potentially very long duty cycle, OMA is not well suited for such schemes. Instead, random medium access (RMA) appears more promising. An RMA scheme is based on transmission of short data packets with random scheduling, which is typically unknown to the receiver. The received signal, which consists of the overlapping packets, can be used for energy harvesting and powering of a relay device. Such an energy harvesting relay may utilize the energy for further information processing and uplink transmission. In this paper, we address the design of a simultaneous information and power transfer scheme based on randomly scheduled packet transmissions and reliable symbol detection. We formulate a prediction problem with the goal to maximize the harvested power for an RMA scenario. In order to solve this problem, we propose a new prediction method, which shows a significant performance improvement compared to the straightforward baseline scheme. Furthermore, we investigate the complexity of the proposed method and its vulnerability to imperfect channel state information. [less ▲]

Random block verification: Improving the Norwegian electoral mix net

in Proc. 5th International Conference on Electronic Voting (EVOTE'12) (2012)

Random Encounters and Information Diffusion about Product Quality

in Journal of Economics and Management Strategy (2022)

Random or Evolutionary Search for Object-Oriented Test Suite Generation?

in Software Testing, Verification and Reliability (2018), 28(4), 1660

An important aim in software testing is constructing a test suite with high structural code coverage – that is, ensuring that most if not all of the code under test has been executed by the test cases ... [more ▼]

An important aim in software testing is constructing a test suite with high structural code coverage – that is, ensuring that most if not all of the code under test has been executed by the test cases comprising the test suite. Several search-based techniques have proved successful at automatically generating tests that achieve high coverage. However, despite the well-established arguments behind using evolutionary search algorithms (e.g., genetic algorithms) in preference to random search, it remains an open question whether the benefits can actually be observed in practice when generating unit test suites for object-oriented classes. In this paper, we report an empirical study on the effects of using evolutionary algorithms (including a genetic algorithm and chemical reaction optimization) to generate test suites, compared with generating test suites incrementally with random search. We apply the EVOSUITE unit test suite generator to 1,000 classes randomly selected from the SF110 corpus of open source projects. Surprisingly, the results show that the difference is much smaller than one might expect: While evolutionary search covers more branches of the type where standard fitness functions provide guidance, we observed that, in practice, the vast majority of branches do not provide any guidance to the search. These results suggest that, although evolutionary algorithms are more effective at covering complex branches, a random search may suffice to achieve high coverage of most object-oriented classes. [less ▲]

Random Phase Center Motion Technique for Enhanced Angle-Doppler Discrimination Using MIMO Radars

in European Signal Processing Conference (EUSIPCO) 2017 (2017, August)

A random Phase Center Motion (PCM) technique is presented in this paper, based on Frequency Modulated Continuous Wave (FMCW) radar, in order to suppress the angle- Doppler coupling in Time Division ... [more ▼]

A random Phase Center Motion (PCM) technique is presented in this paper, based on Frequency Modulated Continuous Wave (FMCW) radar, in order to suppress the angle- Doppler coupling in Time Division Multiplex (TDM) Multiple- Input-Multiple-Output (MIMO) radar when employing sparse array structures. The presented approach exploits an apparently moving transmit platform or PCM due to spatio-temporal transmit array modulation. In particular, the work considers a framework utilizing a random PCM trajectory. The statistical characterization of the random PCM trajectory is devised, such that the PCM and the target motion coupling is minimal, while the angular resolution is increased by enabling the virtual MIMO concept. In more details, this paper discusses sidelobe suppression approaches within the angle-Doppler Ambiguity Function (AF) by introducing a phase center probability density function within the array. This allows for enhanced discrimination of multiple targets. Simulation results demonstrate the suppression angle- Doppler coupling by more than 30 dB, even though spatiotemporal transmit array modulation is done across chirps which leads usually to strong angle-Doppler coupling. [less ▲]

Random Probing Security: Verification, Composition, Expansion and New Constructions

in CRYPTO 2020 (2020)