Seeding the Electrothermal Instability through a Three-Dimensional, Nonlinear Perturbation.

Electrothermal instability plays an important role in applications of current-driven metal, creating striations (which seed the magneto-Rayleigh-Taylor instability) and filaments (which provide a more rapid path to plasma formation). However, the initial formation of both structures is not well understood. Simulations show for the first time how a commonly occurring isolated defect transforms into the larger striation and filament, through a feedback loop connecting current and electrical conductivity. Simulations have been experimentally validated using defect-driven self-emission patterns.

Chronic Glaucoma in Dogs: Relationships Between Histologic Lesions and the Gonioscopic Diagnosis of Pectinate Ligament Dysplasia.

Pectinate ligament dysplasia (PLD) is a common cause of canine glaucoma and the definitive clinical diagnosis is based on gonioscopy. Although the histologic lesions of PLD have been described, it has not been determined whether these changes are specific for PLD or if similar histologic changes can develop as a consequence of secondary glaucoma. The filtration angles of 61 enucleated canine globes with chronic glaucoma were evaluated with light microscopy by 3 examiners who were masked to the clinical history, signalment, and gonioscopic results. A histologic diagnosis of PLD versus non-PLD was determined by each examiner based on previously reported morphologic criteria and compared with the clinical gonioscopic diagnosis. Of the 61 enucleated glaucomatous eyes, 40 were clinically diagnosed with PLD. For all 3 examiners, a histologic diagnosis of PLD corresponded poorly with the clinical diagnosis of PLD (range of kappa score: 0.149-0.269; range of AUC: 0.592-0.621). There was no difference between examiners in their ability to correctly diagnose PLD histologically (P = .978). A fair degree of agreement was noted among examiners in obtaining their suspected histologic diagnosis of PLD (kappa score 0.256). No individual or sets of histologic ICA features were consistent with clinical PLD. The results indicate the histologic ICA changes proposed to be characteristic of PLD are also noted in canine globes affected with chronic secondary glaucoma. Therefore, using routine histologic evaluation, a histologic diagnosis of PLD is not possible in the face of chronic canine glaucoma.

Three-dimensional feedback processes in current-driven metal.

Using three-dimensional (3D) magnetohydrodynamic simulations, we study how a pit on a metal surface evolves when driven by intense electrical current density j. Redistribution of j around the pit initiates a feedback loop: j both reacts to and alters the electrical conductivity σ, through Joule heating and hydrodynamic expansion, so that j and σ are constantly in flux. Thus, the pit transforms into larger striation and filament structures predicted by the electrothermal instability theory. Both structures are important in applications of current-driven metal: The striation constitutes a density perturbation that can seed the magneto-Rayleigh-Taylor instability, while the filament provides a more rapid path to plasma formation, through 3D j redistribution. Simulations predict distinctive self-emission patterns, thus allowing for experimental observation and comparison.

Implementation of extreme ultraviolet spectroscopy on a sheared-flow-stabilized Z pinch.

A diagnostic for extreme ultraviolet spectroscopy was fielded on the sheared-flow-stabilized (SFS) fusion Z-pinch experiment (FuZE-Q) for the first time. The spectrometer collected time-gated plasma emission spectra in the 5-40 nm wavelength (30-250 eV) range for impurity identification, radiative power studies, and for plasma temperature and density measurements. The unique implementation of the diagnostic included fast (10 ns risetime) pulsed high voltage electronics and a multi-stage differential pumping system that allowed the vacuum-coupled spectrometer to collect three independently timed spectra per FuZE-Q shot while also protecting sensitive internal components. Analysis of line emission identifies oxygen (N-, C-, B-, Be-, Li-, and He-like O), peaking in intensity shortly after maximum current (>500 kA). This work provides a foundation for future high energy spectroscopy experiments on SFS Z-pinch devices.

Threshold for thermal ionization of an aluminum surface by pulsed megagauss magnetic field.

The first measurement of the threshold for thermal ionization of the surface of thick metal by pulsed magnetic field (B) is reported. Thick aluminum-with depth greater than the magnetic skin layer-was pulsed with partial differential B/ partial differential t from 30-80 MG/micros. Novel loads avoided nonthermal plasma (from electron avalanche, or energetic particles or photons from arcs). Thermal plasma forms from 6061-alloy aluminum when the surface magnetic field reaches 2.2 MG, in qualitative agreement with numerical simulation results by Garanin et al. [J. Appl. Mech. Tech. Phys. 46, 153 (2005)].

Radiation magnetohydrodynamic simulation of plasma formed on a surface by a megagauss field.

Radiation magnetohydrodynamic modeling is used to study the plasma formed on the surface of a cylindrical metallic load, driven by megagauss magnetic field at the 1MA Zebra generator (University of Nevada, Reno). An ionized aluminum plasma is used to represent the "core-corona" behavior in which a heterogeneous Z-pinch consists of a hot low-density corona surrounding a dense low-temperature core. The radiation dynamics model included simultaneously a self-consistent treatment of both the opaque and transparent plasma regions in a corona. For the parameters of this experiment, the boundary of the opaque plasma region emits the major radiation power with Planckian black-body spectrum in the extreme ultraviolet corresponding to an equilibrium temperature of 16 eV. The radiation heat transport significantly exceeds the electron and ion kinetic heat transport in the outer layers of the opaque plasma. Electromagnetic field energy is partly radiated (13%) and partly deposited into inner corona and core regions (87%). Surface temperature estimates are sensitive to the radiation effects, but the surface motion in response to pressure and magnetic forces is not. The general results of the present investigation are applicable to the liner compression experiments at multi-MA long-pulse current accelerators such as Atlas and Shiva Star. Also the radiation magnetohydrodynamic model discussed in the paper may be useful for understanding key effects of wire array implosion dynamics.

Experimental observation of the stratified electrothermal instability on aluminum with thickness greater than a skin depth.

A direct observation of the stratified electrothermal instability on the surface of thick metal is reported. Aluminum rods coated with 70µm Parylene-N were driven to 1 MA in 100ns, with the metal thicker than the skin depth. The dielectric coating suppressed plasma formation, enabling persistent observation of discrete azimuthally correlated stratified thermal perturbations perpendicular to the current whose wave numbers, k, grew exponentially with rate γ(k)=0.06ns^{-1}-(0.4ns^{-1}µm^{2}rad^{-2})k^{2} in ∼1g/cm^{3}, ∼7000K aluminum.

The role of tissue expansion in reconstruction of the ear.

The following guidelines are suggested for the use of tissue expansion in ear reconstruction based on both personal experience and my evaluation of the reported results of expansion in the hands of other surgeons experienced in ear reconstruction: 1) Cases should be carefully selected to avoid those with excess scarring from previous surgery or trauma as well as avoid the other common contraindications to the use of tissue expansion. 2) In most congenital cases the expander should be placed through a remote incision within the postauricular hairline, and excision of the cartilage vestige delayed until expansion is completed and the framework is ready for placement. 3) A remote valve expander of a crescent shape with a volume of 60-100cc is ideal; low profile expanders may even be safer. 4) The pocket for the expander should be dissected immediately above the fascia and against the cartilage remnant. 5) Rapid expansion should be avoided; ideally injections should be carried out one time each week and with relatively small quantities (5-10cc per injection). 6) At the time of expander removal and placement of the cartilage framework the capsule should be meticulously excised to allow tight skin-cartilage coaptation. This is further enhanced by effective suction drainage following wound closure.

Cysts and cyst-like lesions of the skin and subcutaneous tissue.

Cysts and cyst-like lesions are common occurrences seen in a busy plastic surgical practice. Although many can be treated by surgical excision, they still represent an interesting histologic, etiologic, embryologic, and clinical spectrum. In a number of instances, they require detailed multidiagnostic evaluation and complex surgical approaches to excision. By classifying these cystic masses by age group and anatomic location, the clinician can simplify his or her approach to this group of cutaneous masses.

The role of tissue expansion in pediatric plastic surgery.

The ability to increase available local tissue by controlled soft tissue expansion (TE) has led to a rapid increase in the use of TE in clinical practice. This article reviews some general guidelines when using TE in children and addresses some of the concerns previously expressed regarding the effects of TE on growth in infants and children.

Levator repositioning and palatal lengthening for submucous clefts.

Submucous clefts of the palate may present with velopharyngeal incompetence (VPI) or a history of recurrent otitis media. Many surgeons have favored a pharyngeal flap as primary treatment of the velopharyngeal incompetence associated with this disorder. The increasing number of case reports of sleep apnea and airway compromise associated with pharyngeal flaps prompted the use of levator muscle repositioning with palatal lengthening as initial therapy in 15 patients in an attempt to correct the pathologic anatomy while avoiding the postoperative sequelae. Patients were divided into two groups: group A (N = 8) had surgery before age 2 (11.8 +/- 5.7 months), and group B (N = 7) had surgery after 2 years of age (64.3 +/- 24.2 months). No patient in group A required a secondary operative procedure for velopharyngeal incompetence. Normal speech was obtained in 75 percent (N = 6), and slight velopharyngeal incompetence not requiring secondary correction was obtained in 25 percent (N = 2). Group B obtained less dramatic speech results: normal in 14 percent (N = 1), slight velopharyngeal incompetence in 58 percent (N = 4), and no improvement or severe velopharyngeal incompetence requiring a secondary procedure in 28 percent (N = 2). Patients with preoperative otologic disorders (N = 10) obtained significant improvement in 90 percent of cases (p = 0.002). Early surgical intervention in patients with abnormal speech prior to age 2 appears to result in normal speech in the majority of instances. Late repair with levator repositioning and palatal lengthening provided improved speech in 72 percent of patients.

An approach to excision of congenital giant pigmented nevi in infancy and early childhood.

This paper presents a timely coordinated approach to complete excision of congenital giant pigmented nevi in infancy and early childhood based on a review of 78 patients with giant pigmented nevi of the head and neck, trunk, and/or extremity. Giant pigmented nevi in those selected for review measured from a minimum of 2 percent up to 45 percent total body surface (TBS). Giant nevi of the scalp were treated most effectively using tissue expansion, beginning as early as 3 months of age. Expanded forehead and neck flaps in combination with expanded full-thickness skin grafts were used in early excision of giant pigmented nevi of the face. Giant nevi of the trunk were treated using a combination of abdominoplasty technique, tissue expansion, and split-thickness skin graft, with early "large segment" excision and grafting being the most effective treatment of giant nevi covering the posterior trunk. Giant nevi of the extremities were treated most effectively with excision and graft. Expanded full-thickness skin grafts gave excellent coverage on the hands and feet.

Resection of lymphatic malformation of the scrotum.

It is important for clinicians to consider lymphatic malformations in the differential diagnosis of chronic skin lesions, no matter where they appear anatomically. We report a case of deep surgical excision of an extensive lymphatic malformation of the scrotum using regional flaps from uninvolved scrotal tissue. Removal of the lesion not only allowed the patient more comfort but also may have ultimately cured his symptomatology.

Functional cleft lip repair: a sequential, layered closure with orbicularis muscle realignment.

A lip repair based on anatomic and electric stimulation studies of the orbicularis muscle in unilateral cleft lip has previously been reported by one of the authors. Following some early modifications, this technique has been used on 125 primary lip repairs. The details of the present technique are described here. The advantages of the procedure, in addition to its functional reconstruction of the orbicularis muscle, are in its applicability to clefts of all widths and superior scar formation. The sequential nature of the procedure and freedom from commitment to a fixed, measured pattern at the outset makes the teaching of the method easier and the achievement of a pleasing result more predictable.

Congenital midline nasal muscle with associated nasal deformity.

A case is presented of a congenital nasal deformity consisting of a midline nasal muscle, alar cartilage defect, and partially obstructed nostril. The embryology of nasal development is reviewed, and an attempt is made to explain this unique anomaly.

Dermal and epidermal response to soft-tissue expansion in the pig.

To evaluate the dermal and epidermal response to soft-tissue expansion in the pig, round tissue expanders were placed dorsally under tattooed patterns and inflated over 6 weeks. Surface area, skin thickness, histologic changes, and collagen content were evaluated at 6-week intervals. Epidermal thickening and dermal thinning were observed. Dermal thinning persisted 36 weeks after expansion. Dermal collagen content was decreased, although collagen density remained unchanged. Total collagen content calculated within an expanded square grid increased. These data support a theoretical gain in the dermal layer as well as epidermal layer in response to tissue expansion.

Craniofacial dermoids.

Thirty-two patients with nasal dermal sinuses and cysts were treated during the 10-year period from 1978 to 1987. These patients presented with midline cysts (N = 18) or sinus ostia (N = 14). Only 6 of the 32 patients manifested intracranial extension (19 percent). All the patients with intracranial extension exhibited an intracranial mass on preoperative CT scans. Ten patients with no CT evidence of intracranial mass were noted to have only a fibrous cord extending to the base of the foramen cecum. In 4 of these 10 patients, craniotomy confirmed that there was no intracranial extension of the dermoid. Four other patients presented with sinus ostia at the base of the columella. None of these 4 patients had intracranial extension. Clinical examination and preoperative CT scans provide most of the information needed to determine the nature, course, and extent of these lesions.

Expanded full-thickness skin grafts in children: case selection, planning, and management.

Since our initial presentation of our experience with tissue expansion as a means of harvesting large full-thickness skin grafts in children in 1987, we have continued to "expand" both the size of full-thickness skin grafts harvested and the range of reconstructive problems to which we have applied the technique. Sixteen expanded full-thickness grafts have been used for immediate reconstruction following giant nevus excision and in postburn reconstruction. Patients ranged in age from 6 months to 15 years, with follow-up ranging from 6 months to 6 1/2 years. Grafts ranging in size from approximately 60 cm2 (excluding the dimensions of one submental graft) to greater than 700 cm2 were harvested from expanded donor sites on unilateral or bilateral groin/lower abdomen, clavicular, and a single submental expansion. Five expanded full-thickness grafts were used in facial reconstruction for single aesthetic unit coverage, multiple unit, and one single-sheet full facial graft. One expanded full-thickness graft was used on the breast. Three grafts were used in dorsal hand and finger coverage, and seven were used on the lower extremity, including an entire plantar surface and toes. Graft loss was confined to a 6.25-cm2 area on one cheek in the full facial expanded full-thickness grafts and a 9-cm2 area on the non-weight-bearing area of the full plantar graft. Donor-site complications were negligible. The anatomic confines of the donor sites and size of the patient may require expander replacement (in situ serial expansion) in order to obtain a large enough graft and accomplish primary donor-site closure. Expander and injection port placement in children for ease of injection and planned expander change must be anticipated. Our protocol from preoperative teaching through graft take is reviewed. Experience has demonstrated that expanded full-thickness grafts maintain all the characteristics of non-expanded full-thickness skin grafts and are an excellent reconstructive option in children.

Maintenance of airway patency following treatment of choanal atresia.

Airway patency following repair for choanal atresia is effectively maintained utilizing Argyle polyethylene chest tubes as stents. Retrograde placement of the tubes from the mouth into the nasal passage is accomplished so that once secured, the largest diameter of the tubes is wedged against the posterior portion of the nasal ostium. This approach limits anterior migration of the tubes, preserving the columella and nasal rims while ensuring maintenance of airway patency following treatment of choanal atresia.

Incorporation of the W-plasty in repair of macrostomia.

Macrostomia is an uncommon deformity, the features of which have been outlined. The importance of accurate preoperative marking of the normal landmarks and three-layered repair are stressed. Our technique combines triangular mucosal flaps at the commissure, reconstruction of the oral and buccal musculature, and skin closure using a W-plasty. This skin closure results in a less conspicuous scar while still preventing lateral drift of the commissure. We feel this is an effective surgical procedure that yields consistent clinical results.