Charged-particle multiplicity fluctuations in Pb–Pb collisions at $$\sqrt{s_{\mathrm {NN}}}$$ = 2.76 TeV

Measurements of event-by-event fluctuations of charged-particle multiplicities in Pb–Pb collisions at $$\sqrt{s_{\mathrm {NN}}}$$ s NN $$=$$ = 2.76 TeV using the ALICE detector at the CERN Large Hadron Collider (LHC) are presented in the pseudorapidity range $$|\eta |<0.8$$ | η | < 0.8 and transverse momentum $$0.2< p_{\mathrm{T}} < 2.0$$ 0.2 < p T < 2.0 GeV/c. The amplitude of the fluctuations is expressed in terms of the variance normalized by the mean of the multiplicity distribution. The $$\eta $$ η and $$p_{\mathrm{T}}$$ p T dependences of the fluctuations and their evolution with respect to collision centrality are investigated. The multiplicity fluctuations tend to decrease from peripheral to central collisions. The results are compared to those obtained from HIJING and AMPT Monte Carlo event generators as well as to experimental data at lower collision energies. Additionally, the measured multiplicity fluctuations are discussed in the context of the isothermal compressibility of the high-density strongly-interacting system formed in central Pb–Pb collisions.

Integration Of RFID With WLAN

Radio Frequency Identification (RFID) and Wi-Fi WLANs have achieved widespread applicability in different application domains. However, tag range of RFID systems is very short. Hence, integrating RFID with WLAN networks can contribute to wider application of RFID since Wi-FI nodes have much larger communication range. However, both RFID and WLAN use the same frequency band and incurs interference by [sic] each other for channel utilization. In this thesis, an efficient approach to solve the coexistence and integration problem of RFID and Wi-Fi WLAN is proposed. This solution allows these networks to access the medium in a time sharing manner by making the WLAN Access Point (AP) aware of the RFID neighboring network at the Medium Access Control (MAC) layer. Thus, it is possible to locate and identify the RFID tags in the physical space, with co-located Wi-Fi WLANS. Simulation results show that both networks work together by maintaining the performance such as higher throughput and lower collision probability, as is desired.

Integration Of RFID With WLAN

Radio Frequency Identification (RFID) and Wi-Fi WLANs have achieved widespread applicability in different application domains. However, tag range of RFID systems is very short. Hence, integrating RFID with WLAN networks can contribute to wider application of RFID since Wi-FI nodes have much larger communication range. However, both RFID and WLAN use the same frequency band and incurs interference by [sic] each other for channel utilization. In this thesis, an efficient approach to solve the coexistence and integration problem of RFID and Wi-Fi WLAN is proposed. This solution allows these networks to access the medium in a time sharing manner by making the WLAN Access Point (AP) aware of the RFID neighboring network at the Medium Access Control (MAC) layer. Thus, it is possible to locate and identify the RFID tags in the physical space, with co-located Wi-Fi WLANS. Simulation results show that both networks work together by maintaining the performance such as higher throughput and lower collision probability, as is desired.

Isospin Effect on Baryon and Charge Fluctuations from the pNJL Model

We have studied the possible isospin corrections on the skewness and kurtosis of net-baryon and net-charge fluctuations in the isospin asymmetric matter formed in relativistic heavy-ion collisions at RHIC-BES energies, based on a 3-flavor Polyakov-looped Nambu–Jona–Lasinio model. With typical scalar–isovector and vector–isovector couplings leading to the splitting of u and d quark chiral phase transition boundaries and critical points, we have observed considerable isospin effects on the susceptibilities, especially those of net-charge fluctuations. Reliable experimental measurements at even lower collision energies are encouraged to confirm the observed isospin effects.

Flow and vorticity with varying chemical potential in relativistic heavy ion collisions

We study the vorticity patterns in relativistic heavy ion collisions with respect to the collision energy. The collision energy is related to the chemical potential used in the thermal — statistical models that assume approximate chemical equilibrium after the relativistic collision. We use the multiphase transport model (AMPT) to study the vorticity in the initial parton phase as well as the final hadronic phase of the relativistic heavy ion collision. We find that as the chemical potential increases, the vortices are larger in size. Using different definitions of vorticity, we find that vorticity plays a greater role at lower collision energies than at higher collision energies. We also look at other effects of the flow patterns related to the shear viscosity at different collision energies. We find that the shear viscosity obtained is almost a constant with a small decrease at higher collision energies. We also look at the elliptic flow as it is related to viscous effects in the final stages after the collision. Our results indicate that the viscosity plays a greater role at higher chemical potential and lower collision energies.

Kinetics of the OH + NO₂ reaction: rate coefficients (217–333 K, 16–1200 mbar) and fall-off parameters for N₂ and O₂ bath gases

The radical terminating, termolecular reaction between OH and NO2 exerts great influence on the NOy∕NOx ratio and O3 formation in the atmosphere. Evaluation panels (IUPAC and NASA) recommend rate coefficients for this reaction that disagree by as much as a factor of 1.6 at low temperature and pressure. In this work, the title reaction was studied by pulsed laser photolysis and laser-induced fluorescence over the pressure range 16–1200 mbar and temperature range 217–333 K in N2 bath gas, with experiments at 295 K (67–333 mbar) for O2. In situ measurement of NO2 using two optical absorption set-ups enabled generation of highly precise, accurate rate coefficients in the fall-off pressure range, appropriate for atmospheric conditions. We found, in agreement with previous work, that O2 bath gas has a lower collision efficiency than N2 with a relative collision efficiency to N2 of 0.74. Using the Troe-type formulation for termolecular reactions we present a new set of parameters with k0(N2) = 2.6×10-30 cm6 molecule−2 s−1, k0(O2) = 2.0×10-30 cm6 molecule−2 s−1, m=3.6, k∞=6.3×10-11 cm3 molecule−1 s−1, and Fc=0.39 and compare our results to previous studies in N2 and O2 bath gases.

Kinetics of the OH + NO₂ reaction: Rate coefficients (217–333 K, 16–1200 mbar) and fall-off parameters for N₂ and O₂ bath-gases

The radical terminating, termolecular reaction between OH and NO2 exerts great influence on the NOy / NOx ratio and O3 formation in the atmosphere. Evaluation panels (IUPAC and NASA) recommend rate coefficients for this reaction that disagree by as much as a factor 1.6 at low temperature and pressure. In this work, the title reaction was studied by pulsed laser photolysis-laser induced fluorescence over the pressure range 16–1200 mbar and temperature 217–333 K in N2 bath-gas, with experiments at 295 K (67–333 mbar) for O2. In-situ measurement of NO2 using two optical-absorption set-ups enabled generation of highly precise, accurate rate coefficients in the fall-off pressure range, appropriate for atmospheric conditions. We found, in agreement with previous work, that O2 bath-gas has a lower collision efficiency than N2 with a relative collision efficiency to N2 of 0.74. Using the widely used Troe-type formulation for termolecular reactions we present a new set of parameters with k0(N2) = 2.6 × 10−30 cm6 molecule−2 s−1, k0(O2) = 2.0 × 10−30 cm6 molecule−2 s−1, m = 3.6, k∞ = 6.3 × 10−11 cm3 molecule−1 s−1, Fc = 0.39 and compare our results to previous studies in N2 and O2 bath-gases.

Adaptive Backoff Algorithm for Contention Window for Dense IEEE 802.11 WLANs

The performance improvement in IEEE 802.11 WLANs in widely fluctuating network loads is a challenging task. To improve the performance in this saturated state, we develop an adaptive backoff algorithm that maximizes the system throughput, reduces the collision probability, and maintains a high fairness for the IEEE 802.11 DCF under dense network conditions. In this paper, we present two main advantages of the proposed ABA-CW algorithm. First, it estimates the number of active stations and then calculates an optimal contention window based on the active station number. Each station calculates the channel state probabilities by observing the channel for the total backoff period. Based on these channel states probabilities, each station can estimate the number of active stations in the network, after which it calculates the optimal CW utilizing the estimated active number of stations. To evaluate the proposed mechanism, we derive an analytical model to determine the network performance. From our results, the proposed ABA-CW mechanism achieved better system performance compared to fixed-CW (BEB, EIED, LILD, and SETL) and adaptive-CW (AMOCW, Idle Sense) mechanisms. The simulation results confirmed the outstanding performance of the proposed mechanism in that it led to a lower collision probability, higher throughput, and high fairness.