Energy distribution of the Einstein-Klein-Gordon system for a static spherically symmetric spacetime in (2+1)-dimensions

We use Moeller's energy-momentum complex in order to explicitly compute the energy and momentum density distributions for an exact solution of Einstein's field equations with a negative cosmological constant minimally coupled to a static massless scalar field in a static, spherically symmetric background in (2+1)-dimensions.Comment: 9 pages, 1 figur

FPGA design of low complexity SEFDM detection techniques

This paper presents for the first time the hardware design of low complexity detection algorithms for the recovery of Spectrally Efficient Frequency Division Multiplexing (SEFDM) signals. The work shows that a practical design is feasible using Field Programmable Gate Arrays (FPGAs). Two detection techniques can be implemented using the proposed system architecture, namely Zero Forcing (ZF) and Truncated Singular Value Decomposition (TSVD), demonstrating that our hardware design is flexible. TSVD offers a significant reduction in complexity compared to optimal detection techniques, such as Maximum Likelihood (ML) while outperforming ZF, in terms of Bit Error Rate (BER). Results show excellent fixed-point performance and are comparable to existing floating-point computer-based simulations

Moeller's Energy-Momentum Complex for a Spacetime Geometry on a Noncommutative Curved D3-Brane

Moeller's energy-momentum complex is employed in order to determine the energy and momentum distributions for a spacetime described by a "generalized Schwarzschild" geometry in (3+1)-dimensions on a noncommutative curved D3-brane in an effective, open bosonic string theory. The geometry considered is obtained by an effective theory of gravity coupled with a nonlinear electromagnetic field and depends only on the generalized (effective) mass and charge which incorporate corrections of first order in the noncommutativity parameter.Comment: 12 page

Zero Padding or Cyclic Prefix: Evaluation for Non-Orthogonal Signals

The debate of using zero padding (ZP) instead of a cyclic prefix (CP) for enhancing channel estimation and equalization performance is a recurring topic. This is particularly true for orthogonal signals, such as orthogonal frequency division multiplexing (OFDM). Yet, there are far fewer studies evaluating the impact of ZP and CP in non-orthogonal systems. Such systems have the added complexity of self-induced interference rendering channel estimation and equalization more challenging. For this reason, this work proposes a new channel estimation and equalization technique for non-orthogonal systems, which combines ZP with an orthogonal demodulator. Results show that the multipath components that appear in the ZP part can be used to enhance performance when compared to the CP approach

Experimental Validation of Zero Padding in SEFDM Systems Using Over-the-Air Transmission

Non-orthogonal spectrally efficient frequency division multiplexing (SEFDM) saves bandwidth by compressing the frequency spacing between the subcarriers. This is at the cost of introducing inter-carrier interference (ICI) between the subcarriers. This self-created ICI compounded by the signal degradation caused during wireless propagation in multipath environments, complicates the task of channel estimation and equalisation. Recent studies suggest that combining zero padding (ZP) with SEFDM signals can simplify the challenge of channel estimation and equalisation in the frequency-domain. In this work, we validate experimentally the new ZP scheme through over-the-air transmission of radio frequency (RF) signals. Experimental results prove that using ZP in SEFDM enhances the channel estimation and equalisation accuracy, in comparison to conventional cyclic prefix (CP)-SEFDM. In addition, it is shown that ZP-SEFDM offers robustness against timing offsets

Energy-momentum for a charged nonsingular black hole solution with a nonlinear mass function

The energy-momentum of a new four-dimensional, charged, spherically symmetric and nonsingular black hole solution constructed in the context of general relativity coupled to a theory of nonlinear electrodynamics is investigated, whereby the nonlinear mass function is inspired by the probability density function of the continuous logistic distribution. The energy and momentum distributions are calculated by use of the Einstein, Landau-Lifshitz, Weinberg and M{\o}ller energy-momentum complexes. In all these prescriptions it is found that the energy distribution depends on the mass $M$ and the charge $q$ of the black hole, an additional parameter $\beta$ coming from the gravitational background considered, and on the radial coordinate $r$. Further, the Landau-Lifshitz and Weinberg prescriptions yield the same result for the energy, while in all the aforesaid prescriptions all the momenta vanish. We also focus on the study of the limiting behavior of the energy for different values of the radial coordinate, the parameter $\beta$, and the charge $q$. Finally, it is pointed out that for $r\rightarrow \infty$ and $q = 0$ all the energy-momentum complexes yield the same expression for the energy distribution as in the case of the Schwarzschild black hole solution.Comment: 20 pages, 4 figures, two of the figures changed, Discussion modified accordingly, present version accepted for publication in AHE

Peer assessment of individual contribution in group work: a student perspective

With group work increasing in popularity at universities, students no longer feel it is acceptable to be awarded the same group mark. This presents a significant challenge in awarding an individual mark which reflects unequivocally the time and effort a student has invested in a group project. To address this challenge, a tool to evaluate individual peer assessed contribution (IPAC) has been developed at University College London (UCL). The aim of this paper is to report on the perceptions of students regarding their experience of peer assessment in group work, since these perceptions are key to ensuring that a tool, such as IPAC, is accepted and used effectively by staff and students alike. The views of 133 students were acquired through anonymous surveys and focus groups ranging from first year undergraduate to doctoral students across 12 different departments. Results showed that 92% of students are in favour of peer assessment with a positive trend to using the IPAC tool. Receiving constructive feedback was considered imperative amongst respondents, which in turn should identify clearly the points of error; highlight explicitly the areas for improvement; and thus reflect accurately the mark being awarded. The attributes that students valued to be important when assessing their teammates were, in decreasing order of priority, attendance at meetings, listening and communication, actual contribution to the project deliverables, quality of the work produced, personal circumstances, and finally time management and organization skills. The detailed analysis and conclusions drawn from this study are the focus of this paper