Current saturation and voltage gain in bilayer graphene field effect transistors.

The emergence of graphene with its unique electrical properties has triggered hopes in the electronic devices community regarding its exploitation as a channel material in field effect transistors. Graphene is especially promising for devices working at frequencies in the 100 GHz range. So far, graphene field effect transistors (GFETs) have shown cutoff frequencies up to 300 GHz, while exhibiting poor voltage gains, another important figure of merit for analog high frequency applications. In the present work, we show that the voltage gain of GFETs can be improved significantly by using bilayer graphene, where a band gap is introduced through a vertical electric displacement field. At a displacement field of -1.7 V/nm the bilayer GFETs exhibit an intrinsic voltage gain up to 35, a factor of 6 higher than the voltage gain in corresponding monolayer GFETs. The transconductance, which limits the cutoff frequency of a transistor, is not degraded by the displacement field and is similar in both monolayer and bilayer GFETs. Using numerical simulations based on an atomistic p(z) tight-binding Hamiltonian we demonstrate that this approach can be extended to sub-100 nm gate lengths.

High on/off ratios in bilayer graphene field effect transistors realized by surface dopants.

The unique property of bilayer graphene to show a band gap tunable by external electrical fields enables a variety of different device concepts with novel functionalities for electronic, optoelectronic, and sensor applications. So far the operation of bilayer graphene-based field effect transistors requires two individual gates to vary the channel's conductance and to create a band gap. In this paper, we report on a method to increase the on/off ratio in single gated bilayer graphene field effect transistors by adsorbate doping. The adsorbate dopants on the upper side of the graphene establish a displacement field perpendicular to the graphene surface breaking the inversion symmetry of the two graphene layers. Low-temperature measurements indicate that the increased on/off ratio is caused by the opening of a mobility gap.

The role of assistive devices in the rehabilitation of hearing impairment.

Formal investigation and clinical experience have revealed success in the use of assistive devices in aiding speech understanding where conventional amplification alone has failed. The long-term benefits of this technology are keeping people, particularly the elderly, socially engaged and independent. To accomplish this end, hearing health care professionals have not only to arm themselves with a rapidly advancing, complex array of technical tools, but also to apply them efficaciously. This article provides an overview of these tools, the procedures for using them, the criteria for selecting them, and the resources for obtaining them. A discussion of the various types of assistive devices and their application is followed by a review of the principles for selection and fitting and concludes with a review of the modern role of the hearing health care provider.

Pharyngeal dermoids ("hairy polyps") as accessory auricles.

The purpose of this study is to clarify the origin and nature of so-called hairy polyps or dermoids of the pharynx, which are often thought to be a variant of pharyngeal teratoma. For this purpose, a case is reported of a dermoid polyp involving the middle ear of an infant, the features of multiple examples of pharyngeal dermoid polyps and teratomas received for consultation by the Armed Forces Institute of Pathology are examined, and selected pertinent reports from the literature are reviewed. All three means are used to support the conclusion that these lesions are choristomatous developmental anomalies arising from the first branchial cleft area and that they essentially represent heterotopic accessory "ears" (auricles) without the growth potential of a teratoma.

A surgical solution for the difficult chronic ear.

We all encounter them: difficult chronic ears that seem to confound management efforts and that constitute an unrelenting imposition to the patient. Typically these ears have undergone multiple surgeries and are chronically infected. Such cases are commonly associated with residual or recurrent cholesteatoma. Those rare ears that temporarily respond to therapy promptly recur once treatment is withdrawn. Even the most aggressive nonsurgical protocols fail these patients, who exhibit lifelong social and professional incapacity. They seem to ultimately defy resolution. The purpose of this article is to present a surgical solution to the difficult chronic ear dilemma that emphasizes disease control. Treatment outcome is reviewed in 541 cases. Management pitfalls are analyzed with follow-up, in some cases 20 years.

Ossiculoplasty using the black hydroxylapatite hybrid ossicular replacement prostheses.

The problems of ossicular reconstruction in chronic ear surgery have led to the development of new ossicular replacement prostheses. Improvements in biocompatibility and design led to the development of hydroxylapatite hybrid (HaH) ossicular replacement prostheses. The senior author's (M.E.G.) experience with the Black HaH prostheses is reviewed. Sixty cases are grouped by procedure and prosthesis (19 TORPs and 41 PORPs) with a minimum follow-up of 1 year. Audiometric data are analyzed to determine the success rate in air-bone gap closure. Complication and extrusion rates are reviewed. These results are compared against those obtained using other prostheses using similar criteria, and this report serves as a follow-up on a previous paper on this subject by the senior author.

Heterotopic gastrointestinal cyst of the tongue.

A 6.5-month-old white male presented with a cyst involving the left posterior half of his tongue which partially compromised his airway. A computed tomography scan revealed that the mass also involved the left floor of the mouth. Surgical excision of the mass was performed, and the mass was demonstrated to be a gastrointestinal heterotopic cyst. The clinical and pathological features of this rare lesion are presented and the pathogenesis is discussed.

The management of the cleft lip and palate patient.

We believe that early closure of the hard palate defect with a palatal appliance and surgical closure of the lip and soft palate according to the rule of tens are very important. Delaying the hard palate closure allows for maximal growth of the palatal shelves. We also feel that pressure equalizing tubes placed in the ears at the initial surgical procedure allows for more normal function of the middle ear, less middle ear infections, better hearing, and ultimately better speech. We feel that early closure of the soft palate may decrease velopharyngeal incompetence by normalizing the position of the pterygoid plates. It may also help to reduce serous otitis media by improving eustachian tube function.

Non-ejection cervical spine injuries due to +Gz in high performance aircraft.

The potential for significant neck injuries exists in today's high performance fighter aircraft. The G-loads required to produce injury need not be excessive, nor is experience level necessarily protective. Eight cervical spine injury cases, due to or aggravated by +Gz in F-15 and F-16 aircrew members are reviewed. These include two compression fractures (C5/C7), three left HNP's (C5-6/C6-7), one fracture of the spinous process (C7), one interspinous ligament tear (C6-7), and one myofascial syndrome (C6). Mechanisms of injury and evaluation are discussed. Exercise conditioning may play an important role in prevention and protection. The role of screening X-rays and improving equipment remain as areas where further work needs to be done.

Non-ejection cervical spine fracture due to defensive aerial combat maneuvering in an RF-4C: a case report.

An unusual case report is presented describing an incident in which an RF-4C instructor pilot fractured three cervical vertebrae after impacting the rear canopy top during a negative G defensive maneuver. The pilot subsequently developed an incomplete tetraparesis later in flight and the aircraft had to be recovered by the front seat pilot. No similar cases have ever been reported to the USAF Safety Center or described in the aviation literature.

Kinetics of human chromosome loss from 3T3-human hybrid cells.

Human chromosomes were lost from populations of 3T3-HeLa and 3T3-diploid human fibroblast (HF) hybrids with similar first-order kinetics. Whereas loss began immediately in 3T3-HF hybrids, there was a lag of 5-10 cell divisions before chromosome loss began in 3T3-HeLa hybrids. Human chromosome loss was not affected by aminopterin selection, the use of polyethylene glycol rather than Sendai virus as fusagen, or by the presence of one or two 3T3 genomes. However, when cell division was retarded by growing 3T3-HF hybrids in low serum or at low temperatures, fewer human chromosomes were lost. This suggests that cell cycle traverse is important in chromosome loss. The distribution of human chromosomes among hybrid metaphases indicated that gradual chromosome loss occurred in all hybrids rather than extensive loss from a portion of the hybrids. During the period of chromosome loss, increased numbers of individual asynchronously condensed human chromosomes were randomly distributed among hybrid metaphases.