Current-induced cleaning of graphene

A simple yet highly reproducible method to suppress contamination of graphene at low temperature inside the cryostat is presented. The method consists of applying a current of several mA through the graphene device, which is here typically a few $\mu$m wide. This ultra-high current density is shown to remove contamination adsorbed on the surface. This method is well suited for quantum electron transport studies of undoped graphene devices, and its utility is demonstrated here by measuring the anomalous quantum Hall effect.Comment: Accepted for publication in Applied Physics Letter

Beyond treasuries: A foreign direct investment program for U.S. infrastructure

In his jobs address to a joint session of Congress last week, President Obama returned to a familiar theme: a call for nontraditional infrastructure investment as a generator of economic growth and, ultimately, jobs. The President's frequent references to "private investment" and "fully paid" infrastructure are encouraging, yet there is no assurance that domestic private capital investment alone is sufficient to reverse the degradation of the nation's infrastructure. As host to the largest flows of inward foreign direct investment (FDI), it is time that the United States employs this critical source of capital in tackling the nation's infrastructure deficit

超越国债：美国基础设施的一项外国直接投资项目

在上周国会联合会议的报告中，奥巴马总统又回到了一个熟悉的主题--呼吁非传统的基础设施投资，从而拉动经济和就业增长。总统频繁提到“私人投资”和“全额付讫”的基础设施，但仅依靠国内私人资本投资还不足以扭转国家基础设施的退化。作为最大的FDI东道国，美国应当利用这种重要的资本来源于应对国家基础设施赤字问题

超越国债：美国基础设施的一项外国直接投资项目

在上周国会联合会议的报告中，奥巴马总统又回到了一个熟悉的主题--呼吁非传统的基础设施投资，从而拉动经济和就业增长。总统频繁提到“私人投资”和“全额付讫”的基础设施，但仅依靠国内私人资本投资还不足以扭转国家基础设施的退化。作为最大的FDI东道国，美国应当利用这种重要的资本来源于应对国家基础设施赤字问题

Transport properties of graphene in the high-current limit

We present a detailed study of the high-current transport properties of graphene devices patterned in a four-point configuration. The current tends to saturate as the voltage across graphene is increased but never reaches the complete saturation as in metallic nanotubes. Measurements are compared to a model based on the Boltzmann equation, which includes electron scattering processes due to charged and neutral impurities, and graphene optical-phonons. The saturation is incomplete because of the competition between disorder and optical-phonon scattering

Variation in Severity-Adjusted Resource use and Outcome for Neurosurgical Emergencies in the Intensive Care Unit.

BACKGROUND The correlation between the standardized resource use ratio (SRUR) and standardized hospital mortality ratio (SMR) for neurosurgical emergencies is not known. We studied SRUR and SMR and the factors affecting these in patients with traumatic brain injury (TBI), nontraumatic intracerebral hemorrhage (ICH), and subarachnoid hemorrhage (SAH). METHODS We extracted data of patients treated in six university hospitals in three countries (2015-2017). Resource use was measured as SRUR based on purchasing power parity-adjusted direct costs and either intensive care unit (ICU) length of stay (costSRURlength of stay) or daily Therapeutic Intervention Scoring System scores (costSRURTherapeutic Intervention Scoring System). Five a priori defined variables reflecting differences in structure and organization between the ICUs were used as explanatory variables in bivariable models, separately for the included neurosurgical diseases. RESULTS Out of 28,363 emergency patients treated in six ICUs, 6,162 patients (22%) were admitted with a neurosurgical emergency (41% nontraumatic ICH, 23% SAH, 13% multitrauma TBI, and 23% isolated TBI). The mean costs for neurosurgical admissions were higher than for nonneurosurgical admissions, and the neurosurgical admissions corresponded to 23.6-26.0% of all direct costs related to ICU emergency admissions. A higher physician-to-bed ratio was associated with lower SMRs in the nonneurosurgical admissions but not in the neurosurgical admissions. In patients with nontraumatic ICH, lower costSRURs were associated with higher SMRs. In the bivariable models, independent organization of an ICU was associated with lower costSRURs in patients with nontraumatic ICH and isolated/multitrauma TBI but with higher SMRs in patients with nontraumatic ICH. A higher physician-to-bed ratio was associated with higher costSRURs for patients with SAH. Larger units had higher SMRs for patients with nontraumatic ICH and isolated TBI. None of the ICU-related factors were associated with costSRURs in nonneurosurgical emergency admissions. CONCLUSIONS Neurosurgical emergencies constitute a major proportion of all emergency ICU admissions. A lower SRUR was associated with higher SMR in patients with nontraumatic ICH but not for the other diagnoses. Different organizational and structural factors seemed to affect resource use for the neurosurgical patients compared with nonneurosurgical patients. This emphasizes the importance of case-mix adjustment when benchmarking resource use and outcomes

The environment of graphene probed by electrostatic force microscopy

We employ electrostatic force microscopy to study the electrostatic environment of graphene sheets prepared with the micro-mechanical exfoliation technique. We detect the electric dipole of residues left from the adhesive tape during graphene preparation, as well as the dipole of water molecules adsorbed on top of graphene. Water molecules form a dipole layer that can generate an electric field as large as 10^9 V/m. We expect that water molecules can significantly modify the electrical properties of graphene devices.Comment: to be published in Applied Physics Letter

Parallel measurements of vibrational modes in a few-layer graphene nanomechanical resonator using software-defined radio dongles

Software-defined radio dongles are small and inexpensive receivers well known to amateur radio enthusiasts. When connected to an antenna, they enable monitoring of a wide range of the radio spectrum by conditioning the input signal and transferring a downconverted version of it to a personal computer for software processing. Here, we employ a composite of two such dongles, interfaced with codes written in MATLAB and GNU Radio, as a measuring instrument to study the flexural vibrations of a few-layer graphene nanomechanical resonator. Instead of an antenna, we connect the dongles to the split output of a photodetector used to detect vibrations optically. We first perform a quantitative analysis of the dynamics of the first vibrational mode. We then measure the response of the first two vibrational modes in parallel. To illustrate our technique, we detect changes in the vibrational amplitude of both modes induced by periodic strain modulation with a delay of $\approx1$ ms between measurements. Last, we show that our software-based instrument can be employed to demodulate human voice encoded in the vibrations of our resonator. For parallel measurements of several frequency channels, and provided that the input signal is not too weak, our composite system may offer an alternative to the use of multiple lock-in amplifiers or multiple spectrum analyzers, with the distinct advantage of being cost-effective per frequency channel.Comment: 16 pages, 11 figure