Dumbbell Extension Research Articles

Perspective on the description of viscoelastic flows via continuum elastic dumbbell models

Non-Newtonian fluid mechanics and computational rheology widely exploit elastic dumbbell models such as Oldroyd-B and FENE-P for a continuum description of viscoelastic fluid flows. However, these constitutive equations fail to accurately capture some characteristics of realistic polymers, such as the steady extension in simple shear and extensional flows, thus questioning the ability of continuum-level modeling to predict the hydrodynamic behavior of viscoelastic fluids in more complex flows. Here, we present seven elastic dumbbell models, which include different microstructurally inspired terms, i.e., (i) the finite polymer extensibility, (ii) the conformation-dependent friction coefficient, and (iii) the conformation-dependent non-affine deformation. We provide the expressions for the steady dumbbell extension in shear and extensional flows and the corresponding viscosities for various elastic dumbbell models incorporating different microscopic features. We show the necessity of including these microscopic features in a constitutive equation to reproduce the experimentally observed polymer extension in shear and extensional flows, highlighting their potential significance in accurately modeling viscoelastic channel flow with mixed kinematics.

Epidural Spinal Cord Compression by an Abscess from a Dumbbell Extension of a Non-Osseous Soft Tissue Paravertebral Hydatid Cyst in the Dorsal Region

Background and objectives: Human being may become infested with Echinococcus granulosus, as an intermediate host, ending with the formation of hydatid cyst. Hydatidosis, affecting various parts of human body and should be considered in the differential diagnosis of any cystic mass lesion. Osseous Hydatid cyst is rare; however, it involves the spinal column in half of the cases. In the current study, the epidural hydatid cyst had presented with spinal cord compression due to the formation of an epidural abscess formation. Methods: A young adult housewife lady who had been affected by the parasite, primary paravertebral hydatid cyst, between the seventh and ninth dorsal vertebral levels, presented with spinal cord compression due to epidural abscess lesion. Ultrasound, the contrast magnetic resonance, and computed tomography imaging are standard tests in the diagnostic work-up of the lesion and follow-up of the patient. Appropriate dorsal laminectomy, removal of the hydatid cyst, and the inflammatory epidural cystic compressing tissues were done. Results: Operative intervention had resulted in a dramatic improvement in the patient's condition and reversal of her neurological deficit back to normal; the paravertebral ectocyst size had eventually shrunken and there was no recurrence. The excised tissues that were compressing the dorsal spinal cord proved, Histopathologically, to be inflammatory in its microscopical appearance. Conclusions: Hydatid cyst epidural dumbbell extension may rupture and lead to the formation of an abscess, giving enhancement on contrast magnetic resonance and computed tomography scan studies. To our knowledge, this is the first case to be reported in the literature specifying spinal cord compression by an epidural abscess formation from a paraspinal dumbbell extension of hydatid cyst.

Gingko Leaf Sign: A Classical Imaging Finding in Spinal Meningiomas.

The common imaging features surgeons use to distinguish spinal meningiomas from spinal nerve sheath tumors on magnetic resonance (MR) scans include the presence of the "dural tail sign" on contrast-enhanced MR images, hypointensity of the lesion on T2 sequences, presence of calcifications, lack of extraspinal dumbbell extension, and the lack of cystic changes in the lesion. We highlight the rarely described finding-the "Gingko-Leaf" sign that is caused by the stretched denticulate ligament as it extends laterally, through the tumor, from the compressed spinal cord.

Vertebral artery is an anatomical landmark in the posterior unilateral resection of cervical benign nerve sheath tumors with dumbbell extension of Eden type 2 or 3.

In the cervical nerve sheath tumor (NST) surgery with dumbbell extension of Eden type 2 or 3, selection of anterior, posterior, or combined approach remains controversial. This technical note aimed to propose possible advantages of the posterior unilateral approach (PUA). Methods: Six patients who underwent the surgical treatment of cervical NSTs with dumbbell extension of Eden type 2 or 3 were included. The critical surgical steps included (1) complete separation of extradural and intradural procedures, (2) careful peeling of the neural membranes (epineurium and perineurium) from the tumor surface in the extradural procedure, (3) complete removal of the extradural tumor within the neural membranes, (4) intradural disconnection of tumor origin, and (5) intentional tumor removal up to the vertebral artery (VA), i.e., the VA line. The tumor location of dumbbell extension was Eden types 2 and 3 in two and four patients. Gross total resection was achieved in two patients and intentional posterior removal of the tumor to the VA line was achieved in the remaining four patients. No vascular or neural injuries associated with surgical procedures occurred. Postoperative neurological assessment revealed no symptomatic aggravation in all patients. No secondary surgery was performed during the study period. PUA was safe and less invasive for functional recovery and tumor resection, if the anatomical relationship between the tumor and VA is clearly understood. The VA line is an important anatomical landmark to limit the extent of tumor resection.

Extradural spinal schwannoma in a 5 year old non NF child: A rare entity

Abstract Pediatric spinal schwannomas constitute 2.5-4% of all pediatric spinal tumors. They often occur in the setting of neurofibromatosis type 2 (NF-2) and are almost always intradural (with/without dumbbell extension). Rarely are they confined to extradural space alone. Till date only one case of totally extradural lumbosacral schwannoma in a non NF child has been reported. We here report the second case of totally extradural spinal schwannoma in a non NF child. A five year old female child presented with progressively increasing paraperesis and bladder symptoms, with no clinical features of Neurofibromatosis type I or II. Imaging revealed a dorsolumbar extradural lesion from DV11 to LV1. Patient underwent laminoplasty with total excision of tumour. Intraoperatively, the tumor was confined to extradural space alone. Histopathology confirmed Schwannoma. This case highlights that possibility of schwannomas should be considered as a differential diagnosis for intraspinal extradural tumors even in children without NF.

Surgical Management of Solitary Nerve Sheath Tumors of the Cervical Spine: A Retrospective Case Analysis Based on Tumor Location and Extension

Complete resection of spinal nerve sheath tumors (NSTs) does not always result in significant neurological deficit. The purpose of this retrospective case analysis was to discuss the optimal surgical strategy for spinal NST of the cervical spine. Twenty-four patients who underwent surgery for solitary cervical NST over the past decade were included in this retrospective study. Patients with neurofibromatosis or schwannomatosis were excluded. Seventeen of the 24 cases (70.8%) showed extradural dumbbell extension, most frequently at the C1 or C2 vertebral level. Neurological condition was assessed using the modified McCormick functional schema and sensory pain scale. Total removal of the tumor was achieved in 20 of 24 cases (83.3%). Staged surgery using combined anterior and posterior approaches was applied for 2 of 17 cases with extradural dumbbell extension. Tumor involvement with nerve root fibers critical for upper extremity function (C5–C8) was recognized in 6 of 24 cases (25.0%), with complete resection in all 6 cases. Final assessment of neurological function revealed satisfactory or acceptable recovery in all 6 patients. Spinal NSTs with extradural dumbbell extension are a common condition in the cervical spine. Complete removal of spinal NST of the cervical spine may carry a risk of permanent neurological deficit, but such sequelae appeared to be the exception in the present case analysis. A radical and safe surgical strategy, including staged surgery combining anterior and posterior approaches, should be tailored to the individual case.

Ganglioneuroma: To Operate or Not to Operate

Ganglioneuroma (GN) is a benign, differentiated variety of neurogenic tumor. It is often asymptomatic and may be diagnosed by serendipity. Surgical removal is the treatment of choice. However, it has been suggested that postoperative complications and sequelae might outweigh the benefits of this approach. The purpose of the present study was to examine these issues in a large experience of neural tumors. Patients treated between 1992 and 2012 were retrospectively reviewed. Modern imaging, measurement of catecholamine metabolite excretion and metaiodobenzylguanidine were used for workup. Surgical treatment aimed at complete resection. Complications and sequelae were recorded. Literature was searched for regrowth or malignant transformation of GN. Of 227 patients with neural tumors, 24 were GN patients (12 abdominal, 11 thoracic and 1 cervical with 8 dumbbell extensions). Six children were symptomatic (three with abdominal pain and mass, one with stridor or dysphonia, and one each with anisocoria and opsomyoclonus). However, 18 (75%) were asymptomatic and the diagnosis was incidental. Several tumors were large and involved more than one body space. There were no neurologic symptoms in eight cases with dumbbell extension. Complete resection was achieved in 20 children (83%) whereas gross residual was left in four. Postoperative complications were: Horner syndrome (3 patients), mild scoliosis (1 patient), adhesive bowel obstruction (1 patient) and acute urinary retention (1 patient). There was no evidence of either regrowth or malignant behavior in residual masses left in place after follow-up of 84 (1-194) months. There were a limited number of general minor complications in this series that did not include cases of regrowth or malignant transformation. However, these unfavorable events were occasionally reported in the literature. Since diagnosis of GN cannot be ascertained before removal of the mass, this should remain the aim of the treatment, although limiting the chances of complications to a minimum even if incomplete resection is the price to pay. Nonoperative attitudes should not be recommended in all cases, but they are certainly justified in some.

Dumbbell transport and deflection in a spatially periodic potential

We present theoretical results on the deterministic and stochastic motion of a dumbbell carried by a uniform flow through a three-dimensional spatially periodic potential. Depending on parameters like the flow velocity, there are two different kinds of movement: transport along a potential valley and a stair-like motion oblique to the potential trenches. The crossover between these two regimes, as well as the deflection angle, depend on the size of the dumbbell. Moreover, thermal fluctuations cause a resonance-like variation in the deflection angle as a function of the dumbbell extension.

Dumbbell diffusion in a spatially periodic potential

We present a numerical investigation of the Brownian motion and diffusion of a dumbbell in a two-dimensional periodic potential. Its dynamics is described by a Langevin model including the hydrodynamic interaction. With increasing values of the amplitude of the potential we find along the modulated spatial directions a reduction of the diffusion constant and of the impact of the hydrodynamic interaction. For modulation amplitudes of the potential in the range of the thermal energy the dumbbell diffusion exhibits a pronounced local maximum at a wavelength of about 3/2 of the dumbbell extension. This is especially emphasized for stiff springs connecting the two beads.

Boundary Conditions for the Microscopic FENE Models

We consider the microscopic equation of finite extensible nonlinear elasticity (FENE) models for polymeric fluids under a steady flow field. It is shown that for the underlying Fokker–Planck type of equations, any preassigned distribution on the boundary will become redundant once the nondimensional number $\text{{\it Li\/}} := \frac{Hb}{k_BT} \geq 2$, where H is the elasticity constant, $\sqrt{b}$ is the maximum dumbbell extension, T is the temperature, and $k_B$ is the usual Boltzmann constant. Moreover, if the probability density function is regular enough for its trace to be defined on the sphere $|m| = \sqrt{b}$, then the trace is necessarily zero when $\text{{\it Li\/}} > 2$. These results are consistent with our numerical simulations as well as some recent well-posedness results by preassuming a zero boundary distribution.

Cervical Dumbbell Intra-extradural Hemangioblastoma: Total Removal through the Lateral Approach: Technical Case Report.

Extradural hemangioblastomas account for 8 to 12% of all spinal hemangioblastomas. Among them, intra-extradural forms with a dumbbell extension are extremely rare. We report a case of intra-extradural hemangioblastoma involving the C6 cervical nerve root. The patient was a 31-year-old woman presenting with signs of myelopathy and C6 radiculopathy on the right side. A computed tomographic scan and magnetic resonance imaging demonstrated a dumbbell tumor that had developed through the C5-C6 intervertebral foramen. Angiography revealed a well-circumscribed mass with feeders from the vertebral artery and the deep cervical artery. The tumor was totally removed through the lateral approach, with control of the vertebral artery and sacrifice of the C6 cervical nerve root. Limited bone drilling to enlarge the foramen permitted us to reach and resect the intradural component. Histopathological examination confirmed the diagnosis of hemangioblastoma. Follow-up was uneventful. This is the sixth reported case of a cervical dumbbell hemangioblastoma investigated by computed tomographic scanning and MRI but the first one resected via the lateral approach. The lateral approach seems appropriate for surgical resection because it provides primary control of the vascular feeders and access to the extradural and intradural components.

The behavior of velocity enhancement in microcapillary flows of flexible water-soluble polymers.

A concentration depletion is developed nearby a capillary wall from the result of flow-induced radial migration to the axis region of capillary incorporating with the chain extension. The velocity enhancement factor can be defined quantifying the migration of polymers. For the experimental observation of the radial migration, the capillary hydrodynamic fractionation (CHDF) system has been adopted as a probe on the microcapillary flow of water-soluble flexible polymers. As a practical implication, the migration phenomena may lead to apply this system due to the possible alteration of the elution characteristics. In order to verify the experimental results more accurately, a model has been provided based on the diffusion equation and the conformation-dependent friction involving a radial dependence of hydrodynamic force on the dumbbell extension. For the nonionic polyacrylamide, the experimental behavior of velocity enhancement was shown to be in accordance with the present model within the somewhat increased We. In case of the anionic polyelectrolyte with 30% hydrolyzed polyacrylamide, the increasing slopes of velocity enhancement are different with the eluant ionic strength. Note that the experimental data allow us to consider an enhanced migration due to the long-ranged repulsive force between capillary wall and polymer.

Stresses in Dilute Solutions of Bead-Nonlinear-Spring Macromolecules. III. Friction Coefficient Varying with Dumbbell Extension

The examination of the mechanics of dumbbell suspensions is extended to include the increase of the friction coefficient with molecular extension, both in weak flows and in strong flows. The most interesting result occurs in steady elongational flows where a “hysteresis” loop is found, so that in a certain range of elongation rates two elongational viscosities are possible, the one occurring depending on the previous history of the elongation rate. This result is of interest because it increases the plausibility of those explanations of turbulent drag reduction which depend on maintaining the molecules in an extended, highly dissipative configuration. The hysteresis loop is also of interest in that it represents an effectively infinite memory of a selective type which is not compatible with the usual hypotheses about fading memory usually associated with the simple fluid concepts of continuum mechanics, although our dilute solution model is clearly a simple fluid. No hysteresis loop was found in steady shearing flows, but an increase in viscosity above the zero-shear viscosity is predicted at intermediate shear rates.