11,310 research outputs found
Screening effects in Relativistic Models of Dense Matter at Finite Temperature
We investigate screening effects of the medium on the potential interaction
between two static 'charges' for different models of dense plasmas in the
one-boson exchange approximation. The potential can exhibit an oscillatory
behavior, which is related to the analytic structure of the corresponding boson
propagators in the complex -plane. We have first revisited the one-pion
exchange in a nuclear medium. In addition to Friedel oscillations, which are
associated to branch cuts in the -plane, there appears another oscillatory
component, which arises from a pole on the pion propagator. This pole is
located appart from the axes, giving rise to an oscillating Yukawa-like
potential. Therefore, we call this phenomenon 'Yukawa oscillations'. This
phenomenon does not appear in the Debye component of the QED screened
potential, even if the coupling constant is artificially increased. We have
also studied a model of QCD quark-gluon plasma. In this case, the one-gluon
propagator also shows this kind of poles. At high densities and/or
temperatures, where one expects perturbative QCD to be valid, the pole shifts
towards large momenta.Comment: Revtex. 9 pages, 9 figure
A new upper bound for 3-SAT
We show that a randomly chosen 3-CNF formula over n variables with
clauses-to-variables ratio at least 4.4898 is, as n grows large, asymptotically
almost surely unsatisfiable. The previous best such bound, due to Dubois in
1999, was 4.506. The first such bound, independently discovered by many groups
of researchers since 1983, was 5.19. Several decreasing values between 5.19 and
4.506 were published in the years between. The probabilistic techniques we use
for the proof are, we believe, of independent interest.Comment: 20 page
A low-cost tracking system for running race applications based on bluetooth low energy technology
Timing points used in running races and other competition events are generally based on radio-frequency identification (RFID) technology. Athletes’ times are calculated via passive RFID tags and reader kits. Specifically, the reader infrastructure needed is complex and requires the deployment of a mat or ramps which hide the receiver antennae under them. Moreover, with the employed tags, it is not possible to transmit additional and dynamic information such as pulse or oximetry monitoring, alarms, etc. In this paper we present a system based on two low complex schemes allowed in Bluetooth Low Energy (BLE): the non-connectable undirected advertisement process and a modified version of scannable undirected advertisement process using the new capabilities present in Bluetooth 5. After fully describing the system architecture, which allows full real-time position monitoring of the runners using mobile phones on the organizer side and BLE sensors on the participants’ side, we derive the mobility patterns of runners and capacity requirements, which are determinant for evaluating the performance of the proposed system. They have been obtained from the analysis of the real data measured in the last Barcelona Marathon. By means of simulations, we demonstrate that, even under disadvantageous conditions (50% error ratio), both schemes perform reliably and are able to detect the 100% of the participants in all the cases. The cell coverage of the system needs to be adjusted when non-connectable process is considered. Nevertheless, through simulation and experimental, we show that the proposed scheme based on the new events available in Bluetooth 5 is clearly the best implementation alternative for all the cases, no matter the coverage area and the runner speed. The proposal widely exceeds the detection requirements of the real scenario, surpassing the measured peaks of 20 sensors per second incoming in the coverage area, moving at speeds that range from 1.5 m/s to 6.25 m/s. The designed real test-bed shows that the scheme is able to detect 72 sensors below 600 ms, fulfilling comfortably the requirements determined for the intended application. The main disadvantage of this system would be that the sensors are active, but we have proved that its consumption can be so low (9.5 µA) that, with a typical button cell, the sensor battery life would be over 10, 000 h of use
Anti-Collision Adaptations of BLE Active Scanning for Dense IoT Tracking Applications
Bluetooth low energy (BLE) is one of most promising technologies to enable the Internet-of-Things (IoT) paradigm. The BLE neighbor discovery process (NDP) based on active scanning may be the core of multiple IoT applications in which a large and varying number of users/devices/tags must be detected in a short period of time. Minimizing the discovery latency and maximizing the number of devices that can be discovered in a limited time are challenging issues due to collisions between frames sent by advertisers and scanners. The mechanism for resolution of collisions between scanners has a great impact on the achieved performance, but backoff in NDP has been poorly studied so far. This paper includes a detailed analysis of backoff in NDP, identifies and studies the factors involved in the process, reveals the limitations and problems presented by the algorithm suggested by the specifications and proposes simple and practical adaptations on scanner functionality. They are easily compatible with the current definitions of the standard, which together with a new proposal for the backoff scheme, may significantly improve the discovery latencies and, thus, the probability of discovering a large number of devices in high density scenarios
Spatially resolved kinematics in the central 1 kpc of a compact star-forming galaxy at z=2.3 from ALMA CO observations
We present high spatial resolution (FWHM0.14'') observations of the
CO() line in GDS-14876, a compact star-forming galaxy at with
total stellar mass of . The spatially resolved
velocity map of the inner ~kpc reveals a continous velocity
gradient consistent with the kinematics of a rotating disk with km s and . The
gas-to-stellar ratios estimated from CO() and the dust continuum emission
span a broad range, and
, but are nonetheless consistent given the
uncertainties in the conversion factors. The dynamical modeling yields a
dynamical mass of which is
lower, but still consistent with the baryonic mass, (M=
M + M/M), if the smallest
CO-based gas fraction is assumed. Despite a low, overall gas fraction, the
small physical extent of the dense, star-forming gas probed by CO(),
smaller than the stellar size, implies a strong concentration
that increases the gas fraction up to
in the central 1 kpc. Such a gas-rich center, coupled with a high
star-formation rate, SFR 500 M yr, suggests that
GDS-14876 is quickly assembling a dense stellar component (bulge) in a strong
nuclear starburst. Assuming its gas reservoir is depleted without
replenishment, GDS-14876 will quickly ( Myr) become a
compact quiescent galaxy that could retain some fraction of the observed
rotational support.Comment: Accepted for Publication in ApJL. Kinematic maps are shown in Figures
2 and
Low-cost test measurement setup for real IoT BLE sensor device characterization
The methodology presented in this paper aims to characterize impairments shown by real devices which are usually neglected on standardized tests but that become very important in massive IoT scenarios. For instance, we have measured that real BLE scanners are not able to scan continuously even though they are configured to do so. Besides, we have also found and demonstrated that some manufacturers seem not to apply any backoff mechanism although it is mandatory. These two unexpected behaviors have a significant impact on the performance of massive wireless sensor networks based on BLE. So, it becomes necessary to characterize these and other impairments. The proposed tests are based on device current consumption measurements and their association with the information obtained from upper layers. We describe a new low-cost generic measurement setup and provide all the necessary data (configuration parameters, scripts, etc.) for applying the proposed methodology. As an example, we use it to profile the behavior of Bluetooth Low Energy devices. Furthermore, the proposed setup can also inspire researchers to characterize other wireless technology devices, like Wi-Fi, Zigbee, LoRa, etc
The origin of the Acheulean: the 1.7 million-year-old site of FLK West, Olduvai Gorge (Tanzania)
The appearance of the Acheulean is one of the hallmarks of human evolution. It represents the
emergence of a complex behavior, expressed in the recurrent manufacture of large-sized tools, with
standardized forms, implying more advance forethought and planning by hominins than those required
by the precedent Oldowan technology. The earliest known evidence of this technology dates back to
c. 1.7 Ma. and is limited to two sites (Kokiselei [Kenya] and Konso [Ethiopia]), both of which lack fauna.
The functionality of these earliest Acheulean assemblages remains unknown. Here we present the
discovery of another early Acheulean site also dating to c. 1.7 Ma from Olduvai Gorge. This site provides
evidence of the earliest steps in developing the Acheulean technology and is the oldest Acheulean site in
which stone tools occur spatially and functionally associated with the exploitation of fauna. Simple and
elaborate large-cutting tools (LCT) and handaxes co-exist at FLK West, showing that complex cognition
was present from the earliest stages of the Acheulean. Here we provide a detailed technological study
and evidence of the use of these tools on the butchery and consumption of fauna, probably by early
Homo erectus sensu lato
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