Handover parameter optimization in LTE self-organizing networks

This paper presents a self-optimizing algorithm that tunes the handover (HO) parameters of a LTE (Long-Term Evolution) base station in order to improve the overall network performance and diminish negative effects (call dropping, HO failures). The proposed algorithm picks the best hysteresis and time-to-trigger combination for the current network status. We examined the effects of this self-optimizing algorithm in a realistic scenario setting and the results show an improvement from the static value settings

Elucidation of the Double-Bond Position of Long-Chain Unsaturated Fatty Acids by Multiple-Stage Linear Ion-Trap Mass Spectrometry with Electrospray Ionization

Linear ion-trap (LIT) MS2 mass spectrometric approach toward locating the position of double bond(s) of unsaturated long-chain fatty acids and toward discerning among isomeric unsaturated fatty acids as dilithiated adduct ([M − H + 2Li]+) ions are described in this report. Upon resonance excitation in a LIT instrument, charge-remote fragmentation that involves β-cleavage with γ-H shift (McLafferty rearrangement) is the predominant fragmentation pathway seen for the [M − H + 2Li]+ ions of monoenoic long-chain fatty acids. The fragmentation process results in a dilithiated product ion of terminally unsaturated fatty acid, which undergoes consecutive McLafferty rearrangement to eliminate a propylene residue, and gives rise to another dilithiated adduct ion of terminally unsaturated fatty acid. In addition to the above-cited fragmentation process, the [M − H + 2Li]+ ions of homoconjugated dienoic long-chain fatty acids also undergo α-cleavage(s) with shift of the allylic hydrogen situated between the homoconjugated double bonds to the unsaturated site. These fragmentation pathways lead to two types of CC bond cleavages that are allylic (α-cleavage) or vinylic, respectively, to the proximal CC double bond, resulting in two distinct sets of ion series, in which each ion series is separated by a CH2CHCH (40 Da) residue. These latter fragmentations are the predominant processes seen for the polyunsaturated long-chain fatty acids. The spectrum feature dependent on the position of unsaturated double bond(s) affords unambiguous assignment of the position of double bond(s) of long-chain unsaturated fatty acids

Differentiation of 1-O-alk-1′-enyl-2-acyl and 1-O-alkyl-2-acyl Glycerophospholipids by Multiple-Stage Linear Ion-Trap Mass Spectrometry with Electrospray Ionization

We described linear ion-trap mass spectrometric approaches applying MS3 and MS4 toward to the structural characterization of 1-O-alk-1′-enyl-2-acyl-, 1-O-alkyl-2-acyl-, and diacyl-glycerophospholipids (GPL) as the [M – H]− ions desorbed by ESI in negative-ion mode. Further dissociation of the [lM – H – R2CO2H – polar head group]− ions from the [M – H]− ions of GPL that have undergone the consecutive losses of the fatty acid substituent at sn-2 and the polar head group readily gives the structural information of the radyl group at sn-1, resulting in structural differentiation among the 1-O-alk-1′-enyl-2-acyl-, 1-O-alkyl-2-acyl, and diacyl-glycerolphospholipid molecules. The distinction between a 1-O-alk-1′-enyl-2-acyl- and a 1-O-alkyl-2-acyl-GPL is based on the findings that the MS3 (or MS4) spectrum of the [M – H – R2CO2H – polar head group]− ion from the former compound is dominated by the alkenoxide anion that represents the radyl moiety at sn-1, while the spectrum from the latter compound is dominated by the ion at m/z 135 arising from further loss of the 1-O-alkyl group as an alcohol. Another important notion is that the optimal collision energy required for acquiring the former spectrum is significantly lower than that required for obtaining the latter spectrum. Using the approaches, we are able to reveal the structures of several isobaric isomers in GPL mixtures of biological origin. Because the [M – H]− ions are readily formed by various GPL classes (except glycerophosphocholine) in the negative-ion mode, these mass spectrometric approaches should have broad application in the structural identification of GPLs

Interval type-2 fuzzy sets in supplier selection

Selection of an appropriate supplier is a crucial and challenging task in the effective management of a supply chain. This study introduces a model for solving the supplier selection problem using interval type-2 fuzzy sets. Moreover, the influence of the membership function shape on the results obtained from the model has been investigated on a real-world problem instance tackled by Ordoobadi

Interval type-2 fuzzy sets in supplier selection

Selection of an appropriate supplier is a crucial and challenging task in the effective management of a supply chain. This study introduces a model for solving the supplier selection problem using interval type-2 fuzzy sets. Moreover, the influence of the membership function shape on the results obtained from the model has been investigated on a real-world problem instance tackled by Ordoobadi

Thoughts on Current and Future Research on Agile and Lean: Ensuring Relevance and Rigor

Over the past two decades, research in the area of agile and lean software development has mirrored the strong growth of the use of agile and lean methodologies. However, while these research streams have made a significant contribution in the use of agile and lean methodologies, much of the recent research lacks the rigor and relevance to make an impact in research and practice. For example, many of the studies have not measured the actual use of agile or lean methods nor had a significant theoretical grounding. Furthermore, agile research has not expanded to fully cover emerging opportunities and challenges. A deeper theoretical motivation on agile and lean software development can help demonstrate how the principles of, for example, agile software development, may be transferred to these other areas, and hence, broaden the research’s relevance. This paper provides commentary intended to help push the agile and lean research agenda forward, and outlines three key critieria that future researchers should consider when conducting research on the phenomenon of agile. The paper also provides an example for the use of the criteria, and presents several initial, open research questions that could help increase the use of agile, including the use of agile and lean concepts in other IT and non-IT contexts

Dwarf Galaxies with Ionizing Radiation Feedback. I: Escape of Ionizing Photons

We describe a new method for simulating ionizing radiation and supernova feedback in the analogues of low-redshift galactic disks. In this method, which we call star-forming molecular cloud (SFMC) particles, we use a ray-tracing technique to solve the radiative transfer equation for ultraviolet photons emitted by thousands of distinct particles on the fly. Joined with high numerical resolution of 3.8 pc, the realistic description of stellar feedback helps to self-regulate star formation. This new feedback scheme also enables us to study the escape of ionizing photons from star-forming clumps and from a galaxy, and to examine the evolving environment of star-forming gas clumps. By simulating a galactic disk in a halo of 2.3e11 Msun, we find that the average escape fraction from all radiating sources on the spiral arms (excluding the central 2.5 kpc) fluctuates between 0.08% and 5.9% during a ~20 Myr period with a mean value of 1.1%. The flux of escaped photons from these sources is not strongly beamed, but manifests a large opening angle of more than 60 degree from the galactic pole. Further, we investigate the escape fraction per SFMC particle, f_esc(i), and how it evolves as the particle ages. We discover that the average escape fraction f_esc is dominated by a small number of SFMC particles with high f_esc(i). On average, the escape fraction from a SFMC particle rises from 0.27% at its birth to 2.1% at the end of a particle lifetime, 6 Myrs. This is because SFMC particles drift away from the dense gas clumps in which they were born, and because the gas around the star-forming clumps is dispersed by ionizing radiation and supernova feedback. The framework established in this study brings deeper insight into the physics of photon escape fraction from an individual star-forming clump, and from a galactic disk.Comment: 15 pages, 12 figures, Accepted for publication in the Astrophysical Journal, Image resolution reduced, High-resolution version of this article is available at http://www.jihoonkim.org/index/research.html#sfm

Dwarf Galaxies with Ionizing Radiation Feedback. II: Spatially-resolved Star Formation Relation

We investigate the spatially-resolved star formation relation using a galactic disk formed in a comprehensive high-resolution (3.8 pc) simulation. Our new implementation of stellar feedback includes ionizing radiation as well as supernova explosions, and we handle ionizing radiation by solving the radiative transfer equation rather than by a subgrid model. Photoheating by stellar radiation stabilizes gas against Jeans fragmentation, reducing the star formation rate. Because we have self-consistently calculated the location of ionized gas, we are able to make spatially-resolved mock observations of star formation tracers, such as H-alpha emission. We can also observe how stellar feedback manifests itself in the correlation between ionized and molecular gas. Applying our techniques to the disk in a galactic halo of 2.3e11 Msun, we find that the correlation between star formation rate density (estimated from mock H-alpha emission) and molecular hydrogen density shows large scatter, especially at high resolutions of <~ 75 pc that are comparable to the size of giant molecular clouds (GMCs). This is because an aperture of GMC size captures only particular stages of GMC evolution, and because H-alpha traces hot gas around star-forming regions and is displaced from the molecular hydrogen peaks themselves. By examining the evolving environment around star clusters, we speculate that the breakdown of the traditional star formation laws of the Kennicutt-Schmidt type at small scales is further aided by a combination of stars drifting from their birthplaces, and molecular clouds being dispersed via stellar feedback.Comment: 16 pages, 15 figures, Accepted for publication in the Astrophysical Journal, Image resolution greatly reduced, High-resolution version of this article is available at http://www.jihoonkim.org/index/research.html#sfm