Marine ice-sheet profiles and stability under Coulomb basal conditions

The behavior of marine-terminating ice sheets, such as the West Antarctic ice sheet, is of interest due to the possibility of rapid grounding-line retreat and consequent catastrophic loss of ice. Critical to modeling this behavior is a choice of basal rheology, where the most popular approach is to relate the ice-sheet velocity to a power-law function of basal stress. Recent experiments, however, suggest that near-grounding line tills exhibit Coulomb friction behavior. Here we address how Coulomb conditions modify ice-sheet profiles and stability criteria. The basal rheology necessarily transitions to Coulomb friction near the grounding line, due to low effective stresses, leading to changes in ice-sheet properties within a narrow boundary layer. Ice-sheet profiles ‘taper off’ towards a flatter upper surface, compared with the power-law case, and basal stresses vanish at the grounding line, consistent with observations. In the Coulomb case, the grounding-line ice flux also depends more strongly on flotation ice thickness, which implies that ice sheets are more sensitive to climate perturbations. Furthermore, with Coulomb friction, the ice sheet grounds stably in shallower water than with a power-law rheology. This implies that smaller perturbations are required to push the grounding line into regions of negative bed slope, where it would become unstable. These results have important implications for ice-sheet stability in a warming climate

Metal-Insulator-Like Behavior in Semimetallic Bismuth and Graphite

When high quality bismuth or graphite crystals are placed in a magnetic field directed along the c-axis (trigonal axis for bismuth) and the temperature is lowered, the resistance increases as it does in an insulator but then saturates. We show that the combination of unusual features specific to semimetals, i.e., low carrier density, small effective mass, high purity, and an equal number of electrons and holes (compensation), gives rise to a unique ordering and spacing of three characteristic energy scales, which not only is specific to semimetals but which concomitantly provides a wide window for the observation of apparent field induced metal-insulator behavior. Using magnetotransport and Hall measurements, the details of this unusual behavior are captured with a conventional multi-band model, thus confirming the occupation by semimetals of a unique niche between conventional metals and semiconductors.Comment: 4 pages, 4 figs, data and discussion on bismuth added, final published versio

Reversible writing of high-mobility and high-carrier-density doping patterns in two-dimensional van der Waals heterostructures

A key feature of two-dimensional materials is that the sign and concentration of their carriers can be externally controlled with techniques such as electrostatic gating. However, conventional electrostatic gating has limitations, including a maximum carrier density set by the dielectric breakdown, and ionic liquid gating and direct chemical doping also suffer from drawbacks. Here, we show that an electron-beam-induced doping technique can be used to reversibly write high-resolution doping patterns in hexagonal boron nitride-encapsulated graphene and molybdenum disulfide (MoS2) van der Waals heterostructures. The doped MoS2 device exhibits an order of magnitude decrease of subthreshold swing compared with the device before doping, whereas the doped graphene devices demonstrate a previously inaccessible regime of high carrier concentration and high mobility, even at room temperature. We also show that the approach can be used to write high-quality p–n junctions and nanoscale doping patterns, illustrating that the technique can create nanoscale circuitry in van der Waals heterostructures

2022 SafeTREC Traffic Safety Fact Sheet: Drug-Involved Driving

The use of cannabis, prescription drugs, and other drugs are increasingly prominent on roadways in the United States,where 25.3 percent of the nation’s 38,824 fatalities in 2020 were related to drug-involved driving. Driving can beimpaired by a variety of legal and illegal drugs, substances, and medications. The effect of specific drugs on behaviorand driving skills vary considerably depending on how they act in the brain and are metabolized. They can slow reactiontime, decrease coordination, increase aggressive and reckless driving, impair cognitive function, or cause drowsiness.All of these effects can contribute to crash risk.Studies suggest that poly-drug use or combining alcohol and drugs can inflate the level of driver impairment and crashrisk. There is variation across jurisdictions in the frequency of testing suspected impaired drivers for drugs, consistencyin laboratory drug testing practices, and capacity of law enforcement personnel. Despite challenges in identifyingcausality and impairment, there is general consensus that many drugs impair driving. Preliminary data from an ongoingNHTSA study of alcohol and drug prevalence during the COVID-19 emergency found some significant increases in theprevalence of drugs detected in blood among fatally and seriously injured drivers, motorcyclists, and pedestrians whencomparing the last quarter of 2019 and the first quarter of 2020 to the second, third, or fourth quarters of 2020. As ofFebruary 2022, nearly three-quarters of states, including California, have legalized medical-use of cannabis productsand over one-third allow recreational cannabis, increasing concerns about traffic safety. According to the NationalInstitute on Drug Abuse, aside from alcohol, cannabis is the most frequently detected drug in drivers who are in crashes.Analyses from FARS presented in the drug-impaired program area include fatalities in crashes that involved a driverwho tested positive for a drug that could cause impairment. Analyses from SWITRS presented in this program area referto drug-involvement and include fatal and serious injuries where law enforcement reported the driver to be under theinfluence of drugs. Crashes in the program area are defined as where one or more drivers tested positive for a drug thatcould cause impairment or was reported as driving under the influence of drugs, depending on which data set is used

2019 SafeTREC Traffic Safety Facts: Drug-Impaired Driving

Driving under the influence of drugs is a significant threat to public safety. Various substances can impair cognition, attention, coordination, and other brain functions critical to driving safety. Unlike alcohol, the mechanism for absorption, distribution, and elimination of drugs from the body, as well as cognitive and behavioral effects differ greatly. The use of cannabis, prescription drugs, and other drugs are increasingly prominent on our roadways, where 22.2 percent of the nation’s 37,133 fatalities in 2017 were related to drug-involved driving.&nbsp

2019 SafeTREC Traffic Safety Facts: Alcohol-Involved Driving

While alcohol-involved driving fatalities have fallen significantly in the last three decades, the National Highway Traffic Safety Administration (NHTSA) reports that alcohol-involved driving still comprises a large percentage of traffic injuries and fatalities. On average in 2017, one person died from an alcohol-involved driving collision every 48 minutes. There was a decrease in the numbers of alcohol-involved driving fatalities in the United States between 2016 and 2017. The figures refer to drivers, passengers, bicyclists, and pedestrians fatally killed or seriously injured in an alcohol-involved collision in California in 2017

SafeTRECT Traffic Safety Facts: Motorcycle Safety

In 2016, there were 5,286 motorcycle riders killed on public roadways in the United States, a 5.1 percent increase from 2015. Motorcyclists are at greater risk of injury during collisions—in 2016, motorcyclists were 28 times more likely than passenger car occupants to be fatally injured in a traffic collision, per vehicle miles traveled. In 2016 only 65.3 percent of U.S. motorcyclists wore helmets. In states with universal helmet laws requiring all riders to wear helmets, the known helmet use rate among fatally injured motorcyclists ranged from 66 percent to 100 percent in 2016, while in states without such laws, the rate was lower, ranging widely from 0 percent to 69 percent. In California, which does have a universal helmet law, the known helmet use rate among fatally injured motorcyclists in 2016 was high (95.3 percent). Estimates maintain that helmets saved 308 lives in California in 2016, and 10 additional lives could have been saved if all motorcyclists wore helmets.&nbsp

2021 SafeTREC Traffic Safety Fact Sheet: Distracted Driving

The National Highway Traffic Safety Administration (NHTSA) defines a distraction-affected crash as one where a driver was determined to be distracted at the time of the crash. According to the National Safety Council, mobile devices are among the top distractions for drivers nationwide. Studies have found that talking on cell phones, both handheld and hands-free, increases crash risk by about four times relative to baseline driving. Built-in communication technologies, along with hands-free cell phone technologies, draw attention away from driving. The ability to multitask is a myth, as attention toggles from either driving to vehicle technologies. The longer time one pays attention to the technology, the less time attention is paid to the roadway environment.Historically, road safety efforts focused on changing human behaviors to prevent crashes. The Safe System approach reframes efforts to save lives by expecting crashes to happen and focusing attention on reducing the severity of injuries when a crash occurs. By understanding the nuances of distracted driving crashes, transportation professionals can better address every aspect of crash risks and implement multiple layers of protection to ensure that everyone traveling on California roadways will go safely. Analyses presented in the distracted driving program area are defined by a driver’s inattention to driving due to some other activity. These analyses will focus exclusively on fatalities using the FARS data set as the SWITRS distracted driving data is limited to cell phone use