Space Needle Research Articles

Design and demonstration of a sensing network for full-scale wind pressure measurements on buildings

There is a need for full-scale wind pressure measurements to evaluate the accuracy of peak wind load estimates from wind tunnel measurements, numerical simulations, or building codes. The objective of this study was to design a sensing network for obtaining long-term records of fluctuating wind pressures, and to demonstrate the network’s potential through deployment. A custom data-logger using the BMP388 absolute pressure sensor, which can measure pressure coefficients within ±0.1 at a wind speed of 10 m/s, was designed. The accuracy of the measured statistics was established through comparison with a standard differential sensor in a wind tunnel experiment. A network of 10 motes was deployed on the sloped roof of the 184 m tall Space Needle, obtaining over 1000 h of fluctuating pressure data. The measurements reveal a windward separation region with strong dependency of the approach wind turbulence on the pressure statistics, but positive skewness limits the peak values. The skewness becomes negative near the edge of a second, leeward separation region, resulting in peak factors up to 2.6 times larger than the code-prescribed value of 3.4. The results demonstrate that long-term full-scale measurements provide valuable insight into peak wind pressures and their dependence on approach wind characteristics.

Comparison of measured and LES-predicted wind pressures on the Space Needle

The majority of wind damage is to building envelope components. Large eddy simulations (LESs), which can predict flow fields at high resolution, have significant potential for analyzing component loads. This study aims to (1) demonstrate that LESs can elucidate flow phenomena behind peak pressure loads, and (2) quantitatively compare LESs to full-scale measurements performed on the roof of the 184 m tall Space Needle. The simulations revealed unsteady flow features responsible for pressure signals observed in separation regions and shear layers. Furthermore, predictions for fluctuation pressure coefficients were quantitatively representative of field data. The main discrepancy observed was a more pronounced variability of measured, compared to simulated, shear layer peak pressures. Detailed measurements of the incoming wind field would be needed to further investigate this discrepancy. The results demonstrate the value of joint field measurements and LESs for studying wind effects.

Field Study of Early Implementation of UV Sources and their Relative Effectiveness for Public Health and Safety

ABSTRACT The emergence of COVID-19 and corresponding public health burden has prompted industries to rapidly implement traditional and novel control strategies to mitigate the likelihood of SARS-CoV-2 transmission, generating a surge of interest and application of ultraviolet germicidal irradiation (UVGI) sources as disinfection systems. With this increased attention the need to evaluate efficacy and safety of these types of devices is paramount. A field study of the early implementation of UVGI devices was conducted at the Space Needle located in Seattle, Washington. Six devices were evaluated, including four low pressure (LP) mercury-vapor lamp devices for air and surface sanitation not designed for human exposure and two krypton chloride (KrCl*) excimer lamp devices to be operated on and around humans. Emission spectra and ultraviolet (UV) irradiance at different locations from the UV devices were measured and germicidal effectiveness against SARS-CoV-2 were estimated. Human safety of KrCl* excimer devices was also evaluated based on measured irradiance and estimated exposure durations. Our results show all LP devices emitted UV radiation primarily at 254 nm as expected. Both KrCl* excimers emitted far UVC irradiation at 222 nm as advertised but also emitted at longer, more hazardous wavelengths (228 to 262 nm). All LP devices emitted strong UVC irradiance, which were estimated to achieve three log reduction of SARS-CoV-2 within 10 seconds of exposure at reasonable working distances. KrCl* excimers, however, emitted much lower irradiance than needed for effective disinfection of SARS-CoV-2 (>90% inactivation) within the typical exposure times. UV fluence from KrCl* excimer devices for employees were below the American Conference of Governmental Industrial Hygienists (ACGIH®) Threshold Limit Values (TLVs®) under the reported device usage and work shifts. However photosensitive individuals, human susceptibility, or exposure to multiple UV sources throughout the course of a worker’s day were not accounted for in this study. Caution should be used when determining acceptability of UV exposure to workers in this occupational setting and future work should focus on UVGI sources in public settings.

Social Movement Gains and Losses: Dilemmas of Arena Creation

Social movements never entirely win or lose, nor do they suddenly appear or disappear. Just as their component parts recombine and continue in other forms, so movements have dozens of impacts of various kinds. To make sense of this complexity we propose examining the outcomes of political interactions for a variety of players (including individuals) across a range of arenas. Given the acknowledged tradeoffs and dilemmas of collective action, we would expect packages of outcomes to appear together sometimes; for example, gains in street mobilization may lead to losses in the form of a damaged reputation or police repression. The first step to explaining such patterns is to identify and name them. We examine one of these outcome patterns, the arena-ownership package, through the case of Seattle's historic $15 per hour wage law passed in 2014, the first ever in a major U.S. city. The players who crafted the bill included an avowed Socialist, the owner of Seattle's iconic Space Needle tower, many representatives of the city's labor movement, and the newly elected Democratic Mayor Ed Murray. These diverse players moved through a series of complex arenas to arrive at the legislative outcome. In this case, we find players who create new arenas, rather than only using already-existing arenas. This move is associated with a typical package of gains and losses: increased control for the player on the one hand, but corresponding losses and risks—the alienation of excluded players and increased perception of responsibility. The creating player is blamed for the arena's failures as well as credited with its successes.

The Seattle Space Needle renovation: Acoustical design considerations and challenges at 600 ft above ground level

Built for the 1962 Seattle World’s Fair as a symbol of humanity’s Space Age aspirations, the Seattle Space Needle is one of the most recognizable landmarks in North America. In September 2017, construction commenced for “The Century Project,” a renovation project designed to reveal the tower’s internal structure while expanding and improving its views. This presentation will discuss the acoustical design criteria for the two levels of all-glass, circular observation levels, as well as design approaches for reverberant sound control, sound isolation for key areas, and mechanical system noise control for a proposed fine dining restaurant at the “Loupe” level. The presentation will also include post-construction measurements and several photos during construction and at project completion.

An Operator's Experience of the Loss-of-Resistance Technique in Epidural Injections: An Observational Study.

A successful interlaminar epidural injection relies on correct epidural space needle placement. Most interlaminar epidural steroid injection (ESI) procedures are performed with a blind technique known as loss-of-resistance (LOR) without an imaging guide. This study aims to evaluate the success rate of the LOR technique in interlaminar epidural steroid injection under fluoroscopic control. Patients who underwent interlaminar ESI owing to a history of at least 3 months of chronic low back and leg pain not responding to medications and physical therapies were included in an observational trial. Participants' age was between 27 and 88 years, and they had an American Society of Anesthesiologists physical status of I-III. The patients were placed in a prone position, and a Tuohy needle was introduced at the level of the L5-S1 interlaminar foramen using fluoroscopic image with an anteroposterior view. A lateral view was obtained when the LOR was felt. The procedures that achieved epidural spread by contrast agent in the first attempt were deemed successful. Those that did not and those that had false positive LOR were regarded as unsuccessful. Interlaminar ESİ was administered to 150 patients. The procedure's success and failure rates were 76% (114 patients) and 24% (36 patients), respectively. A total of 58.3% (21 patients) of patients who underwent an unsuccessful procedure had a false LOR, whereas 41.6% (15 patients) of the same group exhibited other causes. Sex, age, and body mass index (BMI) showed no statistical significance in terms of procedural success. There were statistically significant differences in the distance between the skin and the epidural space according to the body mass index groups. The LOR technique identified the epidural space in most epidural procedures. However, in some cases, LOR was shown to be inadequate. Therefore, we suggest that the LOR technique must be supported by imaging such as fluoroscopy during epidural injections.

To Study the Correlation between Estimated Ultrasound Depth and Actual Needle Depth of Epidural Space in Transverse Plane in Parturients Undergoing Cesarean Section

Background and aim: During pregnancy, edema and obesity obscure the anatomical landmark and because of this epidural space identification become difficult by conventional methods. Loose connective tissue also causes false loss of resistance and responsible for failed block and complications. This study was planned for USG (ultrasonography) guided puncture point detection and epidural space depth assessment and its correlation with actual needle insertion depth in obstetric patients. Methods: Sixty four patients of ASA I and II for elective caesarean sections were included in this study. Lumbar space was identified by USG in which ligamentum-flavum with dura mater complex was taken as key structure for assessment of Ultrasound Depth (UD). This was followed by epidural needle insertion at the same marked point and measurement of epidural space Needle Depth (ND) taken. Concordance correlation coefficient and Bland Altman test were used to compare UD and ND. Results: Mean ND and UD were respectively 3.63 ± 043 cm and 3.61 ± 0.17 and these distances were not significantly different (P>0.0001). Bland Altman analysis showed mean of difference between UD and ND to be insignificant (0.02). Significant concordance correlation r=0.96 (95% CI-0.94-0.9, p>0.0001) was observed between ND and UD. Conclusion: In obstetric population pre puncture ultrasound scanning of lumbar spine helps in approximate assessment of epidural space depth and its correlate precisely with actual needle depth.

A new method for pharmaceutical compounding and storage of anti-VEGF biologics for intravitreal use in silicone oil-free prefilled plastic syringes

Intravitreal injections of antibody-based biologics targeting vascular endothelial growth factor (VEGF) are highly effective and have markedly decreased the risk of visual impairment associated with prevalent retinal diseases, such as neovascular age-related macular degeneration and diabetes macular oedema. The diseases are chronic in their nature, and most patients need long-term therapy to suppress disease activity. We previously reported a compounding method for repackaging and storage of aflibercept (Eylea), a commonly used anti-VEGF biologic, in silicone oil-coated plastic syringes without compromising drug stability or activity. In addition to improving safety and time spent per patient, compounding of anti-VEGF biologics enables single-dose vials to be split into multiple syringes, thereby considerably reducing waste and drug expenses. However, symptomatic silicone oil droplets may deposit in the eye’s vitreous body after repetitive injections. To fully avoid this complication, we here report on a novel pharmaceutical compounding method using silicone oil-free syringes and a 33 G × 9 mm Low Dead Space Needle hub injection needle. We evaluate the method for three anti-VEGF biologics commonly used in ophthalmology: aflibercept, ranibizumab (Lucentis) and bevacizumab (Avastin). Our results show that compounding and storage for one week does not compromise the functional activity of the biologics and allows for safe and cost-effective compounding of anti-VEGF biologics for intravitreal injections in prefilled silicone oil-free syringes.

Dredge a River, Make a Nation Great: Shipping, Commerce, and Territoriality in the Detroit River, 1870–1905

The Michigan Historical Review 45:1 (Spring 2019): 27-46©2019 Central Michigan University. ISSN 0890-1686 All Rights Reserved Dredge a River, Make a Nation Great: Shipping, Commerce, and Territoriality in the Detroit River, 1870-1905 By Ramya Swayamprakash Bob-Lo, or Bois Blanc Island, on the Canadian side of the lower Detroit River, is now full of expensive houses. There is no public transportation to or on the island, so to get there you would need to take the car ferry to cross the 1,000-foot channel. If you avoid the houses and go south (in the general direction of the “space needle”), you would enter the remains of Bob-Lo amusement park, which served the area from 1898 until 1994. If you walk to the end of the park, you will get to the head of a long, narrow strip of land. At the end of that strip, with Clifford the family dog’s grave for company, you will see Lake Erie stretching from a mile or so downstream all the way to the horizon. What you probably would not notice is that the long strip of land at the tip of Bois Blanc is all dredged material deposited to create an “upbound” sheltered shipping channel—the one you cross to get on the island in the first place. If you look towards the United States, you will see another sliver of land, covered with trees. That is the tail end of the “downbound” Livingstone Channel, created in the early twentieth century to make lake shipping in the lower Detroit River more efficient by separating it into unidirectional channels. Upstream of Bois Blanc Island and Fort Malden near Amherstburg, Ontario, lies the Limekiln Crossing.1 Dredged since the 1890s, the crossing is the subject of this article. Between 1874 and 1968 (when major dredging operations stopped), construction projects in the Detroit River created 96.5 kilometers (60 miles) of shipping channels, removed over 46,200,000 cubic meters of material, covered 4,050 hectares (40.5 square kilometers) of river bottom with dredge spoils, and built 85 hectares of above-waterline compensating works at a total cost of $283 million, all in the service of commercial 1 Historical sources also refer to the area as “Lime Kiln,” “Limekilns,” and “Limekiln.” For consistency, this article uses “Limekiln Crossing” except when quoting primary sources. 28 The Michigan Historical Review shipping in the Great Lakes.2 Even today, dredging continues as a maintenance act, to keep channels navigable and capable of handling bigger ships with deeper drafts. Dredging is clearly big business. The strip of land on which Clifford rests was constructed in the mid-twentieth century; however, the antecedents of this strip lie in the nineteenth century. This essay conceptualizes dredging as a process that was not merely a technological challenge but also had political underpinnings and territorial ambitions. Dredging is an act of claiming territory through “improvements.” Using the Detroit River in the late nineteenth century as a case study, I contend that dredging involved a process of making place—both physically, as dredge spills created new territory, and in imagination, as dredging helped promote state sovereignty. Dredging exposes the complications of boundary making, territorial control, and commerce. I examine dredging in the Detroit River from 1870 to 1905 for two reasons. First, dredging did not actually begin in the Great Lakes until the second half of the nineteenth century. Second, the possibility of railroad development brought together the shipping industry in its attempt to wield its substantial economic and political clout to stop railroads in their tracks by “improving” the channels through dredging as an important strategy. By 1906, the Detroit-Windsor rail tunnel was under construction. Completed in 1910, the tunnel allowed railroads to bypass the rail ferries that had been the primary means for railroads to cross the river. While the tunnel did not immediately terminate dredging operations, it did present a slow breaking-down of the hegemony of the shipping industry. Between 1870 and 1905, the shipping industry enjoyed almost unparalleled commercial success and political power; thus, this essay also chronicles the heyday of that industry. Why the Detroit River? From the height...

Feasibility of needle and syringe programs in Tajikistan distributing low dead space needles

BackgroundIn 2012, the World Health Organization recommended that needle and syringe programs offer their clients low dead space insulin syringes with permanently attached needles. However, in many countries, these syringes are not acceptable to a majority of people who inject drugs. This study assessed the feasibility of working with needle and syringe programs to implement the WHO recommendation using low dead space detachable needles. The study also assessed the acceptability of the needles.MethodsTwo needle and syringe programs in Tajikistan—one in Kulob and one in Khudjand—received 25,000 low dead space detachable needles each. The programs distributed low dead space detachable needles and a marketing flyer that emphasized the relative advantages of the needles. Each program also enrolled 100 participants, and each participant completed a baseline interview and a 2-month follow-up interview.ResultsAt follow-up, 100% of participants reported trying the low dead space detachable needles, and 96% reported that they liked using the needles. Both needle and syringe programs distributed all their needles within the first 60 days of the project indicating use of the needles, even among clients who did not participate in the study.ConclusionsThis project demonstrates that it is feasible for needle and syringe programs to offer and promote low dead space needles to their clients. The findings indicate that low dead space needles are acceptable to needle and syringe program clients in these Tajikistan cities. To reduce HIV and hepatitis C virus transmission, needle and syringe programs should offer low dead space needles, low dead space insulin syringes in addition to standard needles, and syringes to their clients.

Options for reducing HIV transmission related to the dead space in needles and syringes

BackgroundWhen shared by people who inject drugs, needles and syringes with different dead space may affect the probability of HIV and hepatitis C virus (HCV) transmission differently.MethodsWe measured dead space in 56 needle and syringe combinations obtained from needle and syringe programs across 17 countries in Europe and Asia. We also calculated the amounts of blood and HIV that would remain in different combinations following injection and rinsing.ResultsSyringe barrel capacities ranged from 0.5 to 20 mL. Needles ranged in length from 8 to 38 mm. The average dead space was 3 μL in low dead space syringes with permanently attached needles, 13 μL in high dead space syringes with low dead space needles, 45 μL in low dead space syringes with high dead space needles, and 99 μL in high dead space syringes with high dead space needles. Among low dead space designs, calculated volumes of blood and HIV viral burden were lowest for low dead space syringes with permanently attached needles and highest for low dead space syringes with high dead space needles.ConclusionThe dead space in different low dead space needle and syringe combinations varied substantially. To reduce HIV transmission related to syringe sharing, needle and syringe programs need to combine this knowledge with the needs of their clients.

Effect of Electrode Distance in Grid Electrode: Numerical Models and In Vitro Tests.

Electrochemotherapy is an emerging local treatment for the management of superficial tumors and, among these, also chest wall recurrences from breast cancer. Generally, the treatment of this peculiar type of tumor requires the coverage of large skin areas. In these cases, electrochemotherapy treatment by means of standard small size needle electrodes (an array of 0.73 cm spaced needles, which covers an area of 1.5 cm2) is time-consuming and can allow an inhomogeneous coverage of the target area. We have previously designed grid devices suitable for treating an area ranging from 12 to 200 cm2. In this study, we propose different approaches to study advantages and drawbacks of a grid device with needles positioned 2 cm apart. The described approach includes a numerical evaluation to estimate electric field intensity, followed by an experimental quantification of electroporation on a cell culture. The electric field generated in a conductive medium has been studied by means of 3-dimensional numerical models with varying needle pair distance from 1 to 2 cm. In particular, the electric field evaluation shows that the electric field intensity with varying needle distance is comparable in the area in the middle of the 2 electrodes. Differently, near needles, the electric field intensity increases with the increasing electrode distance and supply voltage. The computational results have been correlated with experimental ones obtained in vitro on cell culture. In particular, electroporation effect has been assessed on human breast cancer cell line MCF7, cultured in monolayer. The use of 2-cm distant needles, supplied by 2000 V, produced an electroporation effect in the whole area comprised between the electrodes. Areas of cell culture where reversible and irreversible electroporation occurred were identified under microscope by using fluorescent dyes. The coupling of computation and experimental results could be helpful to evaluate the effect of the needle distance on the electric field intensity in cell cultures in terms of reversible or irreversible electroporation.

Bill and Melinda Gates Foundation Visitor Center.

The Visitor Center at the new headquarters of the Bill and Melinda Gates Foundation aims to promote awareness of the Foundation’s history, the philanthropic goals of its founders, and its current work in the areas of health, poverty, and education. Located across the street from the Space Needle and other tourist attractions at the sprawling Seattle Center, its interactive exhibits are designed to appeal to tourists and locals, novices and experts, and young and old alike. Although the space without doubt primarily serves a propaganda function for the Foundation and the Gates family, there is much of interest to the historian of medicine. A large portion of the exhibition area, in fact, is devoted to shaping perceptions of the Foundation’s past and ongoing work in public health and global health.

Event-level analyses of sex-risk and injection-risk behaviors among nonmedical prescription opioid users

ABSTRACTBackground: Nonmedical prescription opioid use has been linked to hepatitis C virus (HCV) infection among people who inject drugs and with using high dead space syringes that retain more blood and transfer more HIV if shared. Little is known regarding its effects on sex-risk behaviors. Objectives: This paper examines event-level associations between nonmedical prescription opioid use and sharing high dead space syringes (injection risk) and unprotected intercourse (sex risk) behaviors. Methods: We recruited 1,985 participants from two overlapping risk groups—drug users and men who have sex with men (MSM)—and their sex partners. Participants completed an interview that included event-level sex questions with recent sex partners and injection questions with recent injection partners. We used multivariable generalized estimating equations (GEE) to assess the associations between nonmedical prescription opioid use and unprotected intercourse during sexual encounters and sharing syringes during injection episodes, while adjusting for within-person correlations. Results: When both partners used nonmedical prescription opioids, its use was independently associated with unprotected intercourse in sexual encounters (OR = 2.24; 95% CI = 1.12, 4.49). The use of nonmedical prescription opioids was also associated with sharing high dead space syringes during injection episodes (OR = 6.57; 95% CI = 1.63, 26.51). Conclusion: Nonmedical prescription opioid use is associated with an increase in the risk of unprotected sex and sharing high dead space syringes. HIV and HCV prevention interventions for nonmedical prescription opioid users should address sex-risk behaviors and encourage the use of acceptable low dead space needles and syringes.

“A City of the Future”:Gravity’s Rainbowand the 1962 Seattle World’s Fair

Drawing on archival sources, I argue that the 1962 Seattle World’s Fair (also known as Century 21) was an important source for Thomas Pynchon’s surreal depictions of the Raketen-Stadt in Gravity’s Rainbow. Accounts of the influence of Seattle on Pynchon have been limited to his work as a Boeing technical writer, and Century 21 goes unmentioned in work on the novel’s allusions by Steven Weisenburger and others. Pynchon responds throughout Gravity’s Rainbow to Century 21, particularly its Cold War views of space-age futurism and nuclear weapons. I draw new connections between the angel of Lübeck and John Glenn’s World’s Fair appearance; aspects of the Raketen-Stadt and the fair’s US Science Pavilion; and Pynchon’s many towers and elevators and that signature feature of Century 21, the Space Needle. The conclusion attends to the fair’s traces in Against the Day and Bleeding Edge, demonstrating Pynchon’s nearly career-long fascination with the event.

An Architecture for the Electronic Church: Oral Roberts University in Tulsa, Oklahoma.

More than a university, Oral Roberts University in Tulsa, Oklahoma, was also the headquarters for evangelist Oral Roberts's electronic church. The electronic church in America, dominated by Christian evangelicals, used technology to spread the Gospel over radio airways and television signals to a dispersed audience. Yet evangelicals like Roberts also constructed ambitious campuses in real space and time. The architecture of Oral Roberts University visualized a modern and "populuxe" image for the electronic church in the 1960s and 1970s. The university's Prayer Tower purposely alluded to the Seattle Space Needle, aligning religion and the Space Age, and the campus's white, gold, and black color palette on late modern buildings created an image of aspirational luxury, conveying Roberts's health and wealth gospel. Oral Roberts University served as a sound stage for Roberts's radio and television shows, a pilgrimage point for his audience, and a university dedicated to training evangelicals in the electronic church.

Factors that influence the characteristics of needles and syringes used by people who inject drugs in Tajikistan.

Background“Low dead space” syringes with permanently attached needles retain less fluid, blood, and HIV after use than standard “high dead space” syringes. This reduces the probability of HIV transmission if they are shared by people who inject drugs (PWID). The World Health Organization recently recommended that needle and syringe programs (NSP) offer clients low dead space syringes. The success of this recommendation will depend on PWID switching to low dead space needles and syringes. This paper examines the needles and syringes that PWID in Tajikistan use and factors that influence their choices.MethodsIn May 2014, we conducted six focus groups in Kulob and six in Khorog, Tajikistan, with a total of 100 participants. NSP staff members recruited participants. Focus group topics included the needles and syringes used and factors that influence choice of needles and syringes. Focus groups were conducted in Russian and Tajik, audio recorded, transcribed, and translated into English. The translated files were imported into NVivo 10 for coding and analysis.ResultsAll participants in both cities were male and reported injecting heroin. Everyone also reported using syringes with detachable needles almost exclusively. The most popular syringe sizes were 2 and 5 ml. Needles ranged in gauge from 25 to 21 g. Needle gauge was influenced by the size of the vein, the viscosity of drug solution to be injected, and problems with blood clotting. Needles ranged in length from 12 to 38 mm, with 25 and 32 mm being the most popular. Needle length was influenced by the depth of the vein being used. Many PWID inject volumes of fluid greater than 1 ml into deep veins that require needles at least 25 mm long and 25 g in diameter.ConclusionMost low dead space syringes are 1-ml insulin syringes with 12 mm 28 g permanently attached needles. Findings from this project suggest that these will not be acceptable to PWID who need larger syringes and longer and thicker needles that are detachable. Low dead space detachable needles appear to be an acceptable option that could overcome barriers to the widespread use of low dead space equipment for reducing HIV and HCV transmission.

Descriptions Which Have Grown Capital Letters

AbstractAlmost entirely ignored in the linguistic theorising on names and descriptions is a hybrid form of expression which, like definite descriptions, begin with ‘the’ but which, like proper names, are capitalised and seem to lack descriptive content. These are expressions such as the following, ‘the Holy Roman Empire’, ‘the Mississippi River’, or ‘the Space Needle’. Such capitalised descriptions are ubiquitous in natural language, but to which linguistic categories do they belong? Are they simply proper names? Or are they definite descriptions with unique orthography? Or are they something else entirely? This article assesses two obvious assimilation strategies: (i) assimilation to proper names and (ii) assimilation to definite descriptions. It is argued that both of these strategies face major difficulties. The primary goal is to lay the groundwork for a linguistic analysis of capitalised descriptions. Yet, the hope is that clearing the ground on capitalised descriptions may reveal useful insights for the on‐going research into the semantics and syntax of their lower‐case or ‘the’‐less relatives.

A co-operative effect of closely spaced intruding objects puncturing into a soft solid.

When two or more closely spaced indenters puncture a soft solid, the puncturing load diminishes from that required when they are far apart. We have developed a method to examine this effect by embedding a planar tracer grid within a block of an elastic gel and by driving closely spaced syringe needles of different inter-tip spacing through this plane. These experiments show that in addition to a primary crack ahead of the needle-tip, there occurs also a periodically appearing secondary radial crack from its side. The strain field around the side crack remains non-monotonic with a characteristic length scale which varies with both solid modulus and needle diameter. For closely spaced multiple indenters the overlapping strain profiles cause compressive stress at the vicinity of the needles, which arrest the side cracks, the diminishing effect of which leads to stress concentration for the primary crack and the resultant decrease in required load for driving the indenters through the solid. We have shown that such a co-operative effect remains valid for materials of different types, e.g. brittle and ductile and for multiple-tip needles consisting of constituent tips of equal and unequal diameters.

Subarachnoid space needle manipulations for successful block.

Subarachnoid space needle manipulations for successful block.