Distributed, Modular, Network Enabled Architecture For Process Control Military Applications

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Ashish Dubey et al Int. Journal of Engineering Research and Applications ISSN : 2248-9622, Vol. 4, Issue 2( Version 1), February 2014, pp.337-340 RESEARCH ARTICLE www.ijera.com OPEN ACCESS Distributed, Modular, Network Enabled Architecture For Process Control Military Applications Abhijit Kamble*, Ashish Dubey**, C L Waghmare*, Rajesh Chary*, Arun Barde*, Moiz Chasmai*, Guru Prasad* *(Research & Development Establishment (Engineers), DRDO, Pune) **(Research & Development Establishment (Engineers), DRDO, Pune) ABSTRACT In process control world, use of distributed modular embedded controller architecture drastically reduces the number and complexity of cabling; at the same time increases the system computing performance and response for real time application as compared to centralized control system. We propose a design based on ARM Cortex M4 hardware architecture and Cortex Microcontroller Software Interface Standard (CMSIS) based software development. The ARM Cortex-M series ensures a compatible target processor and provides common core peripherals whereas CMSIS abstraction layer reduces development time, helps design software reusability and provides seamless application software interface for controllers. Being a custom design, we can built features like Built-In Test Equipment (BITE), single point fault tolerance, redundancy, 2/3 logic, etc. which are more desirable for a military applications. This paper describes the design of a generic embedded hardware module that can be configured as local I/O controller or application controller or Man Machine Interface (MMI). This paper also proposes a philosophy for step by step hardware and software development. Keywords—COTS; ARM; Cortex; Ethernet; CMSIS I. INTRODUCTION The first industrial plants automation projects, developed in the 1970s, used electrical logic hard-wired into cabinets. These cabinets commanded all electrical equipment located in the plant, and contained all logic needed to perform any operating sequence. Cabinets were modular and composed of local panels, each of which acquired several input signals, and the outputs were set according to hardwired logic. Usually, no communication was established between these panels [1]. Change in requirement needs redevelopment of system. One possible way to cope with this problem is the use of programmable logic controllers (PLCs) and field I/Os. These devices are easily reconfigurable and can be adapted to a variety of situations. In MIL Grade systems, there are two schools of thoughts one is to use centralised control system based on COTS architecture and other is to use completely distributed architecture. Use of standard and off-the-shelf products (COTs) for centralised control based on CPCI and VME architecture lowers the development cost, but usually raises production cost. The COTs products based on distributed/ remote I/Os are available but do not meet MIL specifications. Unavailability of such hardware is the genesis of distributed, modular, network enabled architecture. Today’s embedded market has lot more to offer; from PIC to PowerPC/x86 architectures. www.ijera.com However, ARM architecture has grown with the fastest pace in last 5 years and has become a de-facto Industry standard in the embedded development. ARM has further refined and customised their architecture and come up with specific processors for bare metal to Operating System based applications. This architecture also ensures a compatible target processor and provides common core peripherals. A systematic software development life cycle needs to be followed for development of applications on such a complex hardware. Development of such software is acknowledged as a major cost factor by the embedded industry. The cost and efforts can be reduced by standardization of the software. The ARM Cortex architecture provides us an opportunity to do this by using CMSIS. A consortium of all the ARM silicon vendors ensures optimized, accurate and timely availability of CMSIS libraries. Major thrust for our research was to design and develop MIL grade network enabled embedded controller hardware with modular and reusable software. We can develop variety of control systems for numerous process control applications using these ingredients. 337 | P a g e Ashish Dubey et al Int. Journal of Engineering Research and Applications ISSN : 2248-9622, Vol. 4, Issue 2( Version 1), February 2014, pp.337-340 II. SYSTEM DESCRIPTION 1. System Block Diagram We have designed ARM Cortex based, network enabled, and configurable embedded controller modules. A module can be configured as Application Controller or Intelligent I/O Controller or MMI Controller. A control system can be built using these modules communicating over Ethernet/ RS485/ CAN backbone network as shown in Fig. 1, which can be used for variety of process control applications. The master application software will run on Application Controller; the heart of the control system. The Intelligent I/O Controller will be used for acquiring sensors data and controlling the actuators. The MMI Controller will be used for reading the switches and displaying the status of various activities. The number of modules and their role depends on the system requirements. 2. Architecture of Network Enabled Embedded Controller The concept of the distributed controller is based on networked memory sharing architecture. Each embedded controller module will have two Cortex processors, both interfaced to a dual port RAM in such a way that both can simultaneously read and write to any memory location of the RAM. One of the processor will run Network Interface application called as Network Processor and the other one called Application processor will run Control, MMI or I/O application, based on the system requirements. Fig. 2 shows the detailed internal architecture of this embedded controller hardware. The Application processor will provide all standard interfaces to the outside world through discrete, analog, PWM, Quadrature encoder and serial I/Os. It will also have a dedicated interface for LCD and Debug/Trace. The Network processor shall have Ethernet/ RS485/ CAN bus interface. It will have add-on power supply module which can be selected based on the module power requirement. www.ijera.com III. SELECTION OF PROCESSOR The selection of right device on which to base our design was a challenging task; typically in the scenario where there is a need to have a right balance of price, performance and power consumption [2]. The x86(intel) and PowerPC processors are proven architecture which are currently being used. The ARM offers goodness of 32 bit processing and peripherals on a single chip (SoC) which makes the hardware design extremely simple. ARM eliminates the monopoly of a single silicon vendor as it is an IP core company with a huge silicon vendor base. Hence ARM was an obvious choice for this architecture. We carried out comparative studies of different ARM flavors from different silicon vendors for parameters like processing power, latency, peripherals, support for floating point arithmetic, support for DSP functions and defined road map of at least 10 years. Fig.2. Internal Architecture of Embedded Controller Fig. 3. ARM Processors Chart [3] Fig.1. System Block Diagram www.ijera.com Fig. 3. shows the comparative chart for various ARM Processors for its capability, performance and functionality. Cortex-A series offer high performance processor for Operating System (OS), mainly used for smart phones and PDA applications. Cortex-R series offer exceptional performance processor for real time applications. The consistent interrupt handling structure and programmer's model of Cortex-M series provides a full upwards-compatible path for processors from Cortex-M0 to Cortex-M4. 338 | P a g e Ashish Dubey et al Int. Journal of Engineering Research and Applications ISSN : 2248-9622, Vol. 4, Issue 2( Version 1), February 2014, pp.337-340 Theoretically we should have chosen Cortex-R family for MIL applications. As Cortex-M4 has same performance as Cortex-R with wider silicon vendor support, we opted for Cortex-M4 over Cortex-R. The comparison of Cortex-M family is given in Fig. 4. LPC4350 Dual Core Cortex M4 & Cortex M0 (204MHz) [4] has been selected for Application/ IO/ MMI Controllers. IV. SOFTWARE DEVELOPMENT APPROACH Creation of software is acknowledged as a major cost factor by the embedded industry. The cost is significantly reduced by standardizing the software interfaces across all Cortex-M silicon vendor products, especially while creating new projects or migrating from existing software to a new device. The Cortex-M4 architecture offered us an additional advantage in software development through its Cortex Microcontroller Software Interface Standard (CMSIS). It is a vendor-independent hardware abstraction layer for the Cortex-M processor series. All the major silicon vendors are part of a consortium which has standardized the software interfaces and are bound to release CMSIS libraries for the processors they are producing. The CMSIS enables consistent and simple software interfaces to the processor and the peripherals, simplifying software re-use, reducing the learning curve for new microcontroller developers and reducing the time to market for new devices. CMSIS architecture is shown in Fig. 5. The CMSIS consists of the following components: 1. Peripheral Register and Interrupt Definitions: A consistent interface for device registers and interrupts. 4. www.ijera.com System View Description (SVD): XML file that describes the device peripherals and interrupts. [3] As shown in Fig. 6, a typical control application will consists of following software modules: (1) I/O Read/Write, (2) Communication, (3) Diagnostic/ Monitoring, (4) Typical Control Algorithm, (5) User Interfaces, (6) Timing/ Event/ Exception Handling, (7) Data Logging. These modules are identified based on the applications, i.e., Control, MMI, I/O and Network Interface. These software modules are either completely or partially reusable. Keil Microcontroller Development Environment will be used as a platform for software development, as it provides tool support for CortexM series and widely used by the embedded industry all across the globe [5]. However, another widely used software development platform - Labview, which takes graphical code and generates procedural c code, can also be used in traditional programming environment [6]. Fig. 5. CMSIS Architecture [7] Fig. 4. Cortex M Family Comparison [3] 2. 3. Core Peripheral Functions: Access functions for specific processor features and core peripherals. DSP Library: Optimized signal processing algorithms and for Cortex-M4 support of SIMD instructions. www.ijera.com Fig. 6. Typical Software Module 339 | P a g e Ashish Dubey et al Int. Journal of Engineering Research and Applications ISSN : 2248-9622, Vol. 4, Issue 2( Version 1), February 2014, pp.337-340 V. SUMMARY After studying the theoretical aspects of various architectures, we arrived at the conclusion that ARM Cortex-M4 Processor is best suited for our application. The concept of the distributed controller based on networked memory sharing architecture will certainly help in developing a more efficient control system in the field of military control applications. CMSIS software development standard shall be used to develop the software application for the system. It is quite obvious that in future this architecture will become pervasive because of its features like modularity, inter-changeability, space saving, low latency, connectivity with external networks and scalability which are unattainable with the traditional architecture. The design and architecture discussed in the paper will certainly help in developing process control applications in industrial and military environments. VI. FUTURE SCOPE OF WORK In future, the hardware will be realized using MIL Grade components and proper care will be taken in packaging in order to withstand harsh environmental conditions. Subsequently, the designed controller will be evaluated for different military process control applications. Also a future roadmap for system up-gradation will be developed. Keys issues such as real time response, synchronization, reliable communication of different controllers, power consumption management, www.ijera.com www.ijera.com cooperation, coordination, and security needs to be looked into in the future development. VII. ACKNOWLEDGMENT We are grateful to Dr. S. Guruprasad, Director R&DE (E), DRDO, Pune, India for allowing us to publish this work. We are also thankful to VV Parlikar and AN Ansari for their constant encouragement and scientific discussions. REFERENCES [1] [2] [3] [4] [5] [6] [7] Juan Garcia, Francisco Rogelio Palomo, Antonia Luque,Jose M Quero, Daniel Carrion, Francisco Gamiz, “ Reconfigurable Distributed Network Control System for Industrial Plant Automation” IEEE Transctions on Industrical Electronics, Vol.51 No.6, December 2004. Frederic Gaillard, MCU VS MPU, pg. 1, atmel.com www.emcu.it/CortexFamily/CortexFamily.h tml www.nxp.com/documents/datasheet/lpc4350 _30_20_10.pdf www.keil.com/arm/mdk.asp www.arm.com/products/processors/cortexm/cortex-microcontroller-softwareinterface-standard.php www.eeweb.com/company-blog/arm/thechoices-for-programming-arm-cortex-mmicrocontrollers/ 340 | P a g e ONE | DOI:10.1371/journal.pone.0113644 November 26, 2014 5 / 14 Backward Adjustable Thoracic Support Figure 3. Experimental setup. The picture shows the experimental setup with experimental wheelchair, ultrasound-based motion analysis system, and miniature ultrasonic modules. The first belt with triple markers TS-LD was situated around the level of the posterior superior iliac spines and the anterior superior iliac spines. The second belt with triple markers TS-LU was placed firmly around the T12 level. The third belt with triple markers TS-CR2 was placed firmly around the T1 level. doi:10.1371/journal.pone.0113644.g003 in preamplifier (gain 51000). The EMG system bandwidth was 7 bits 500 Hz, and the common mode rejection ratio was 110 dB. Before the EMG measurement, in order to reduce skin impedance, the skin of electrode site was cleaned with alcohol, shaved with a razor, and lightly abraded with a fine sandpaper. Pairs of self-adhesive Ag-AgCl surface electrodes (Meditrace 100 series; Covidien, Massachusetts, United States) with an inter-electrode distance of 2.5 cm were placed in parallel to the test muscles on both sides. The electrodes were taped on superficial lumbar multifidus (LM: L5 level, parallel to a line connecting the PSIS and L1–L2 interspinous space) [25], lumbar erector spinae (LES: 3 cm lateral to the L3 spinous process) [26], iliocostalis lumborum pars thoracis (ICLT: level of the L1 spinous process, midway between the midline and lateral aspect of the participant’s body) [27], and thoracic erector spinae at the T9 level (TES: 5 cm lateral to the T9 spinous process) [26] on the left (-L) and right (-R) side. A reference electrode was placed on the right iliac crest. For the normalization of EMG data, the aforementioned muscles were normalized to maximal voluntary isometric contraction (MVIC). The full details PLOS ONE | DOI:10.1371/journal.pone.0113644 November 26, 2014 6 / 14 Backward Adjustable Thoracic Support Figure 4. The back attachment placement and angle definition. The angular values of spinal regions were then defined for the following: pelvic (the first belt (PSISs & ASISs) relative to the horizontal line), lumbar (the second belt (T12) relative to the first belt (PSISs & ASISs)), and thoracic (the third belt (T1) relative to the second belt (T12)). doi:10.1371/journal.pone.0113644.g004 of these normalization procedures have been outlined in highly reliable studies [27–29]. The raw EMG data were processed by using the customized software program MATLAB (MATLAB, version7.7; The MathWorks, Massachusetts, United States). The raw data were first checked and removed for the heartbeat and other artifacts by using a customized program in MATLAB. Then, the raw data were demeaned, full wave rectified, filtered by using a fourth-order Butterworth filter with a cut-off PLOS ONE | DOI:10.1371/journal.pone.0113644 November 26, 2014 7 / 14 Backward Adjustable Thoracic Support frequency of 4 to 400 Hz, and a 25 ms moving window was applied to the linear envelope [28]. Statistical Analysis The Statistical Package for the Social Sciences (SPSS, version 21; IBM North America, New York, United States) was used for conducting all statistical analyses. All parameters, including spinal curvatures (pelvic, lumbar, and thoracic angles) and back muscle activations (MVIC of the LM-L, LM-R, LES-L, LES-R, ICLT-L, ICLT-R, TES-L, and TES-R) were compared among the four different sitting postures by using a one-way analysis of variance with repeated measures. The Tukey’s post hoc test (if Levene’s test was not significant) or Games-Howell post hoc test (if Levene’s test was significant) was used for detecting statistically significant differences in the dependent variables across the tests. The statistical significance was set at P,0.05. Results All the participants completed the spinal curvature and back muscle activation measurements using the experimental wheelchair in the SS, NS, LSS, and BTS postures. None reported adverse reactions to the experimental protocol. Spinal Curvature The results of the spinal curvature measurements are shown in Figure 5. In contrast with the SS posture, the NS, LSS and BTS postures appeared to yield significantly lower pelvic and lumbar angle values (P,0.001). When compared with the NS posture, the LSS posture appeared to yield significantly lower pelvic Figure 5. The results of spinal curvature measurement. Comparison of mean pelvic, lumbar, and thoracic angles across 4 sitting postures, which include the slumped (SS), normal (NS), lumbar support (LSS), and backward adjustable thoracic support (BTS) sitting postures. The positive value (+) represents the posterior tilt or kyphosis while the negative value (-) represents the anterior tilt or lordosis. Error bars indicate SD and * indicates p,0.05. doi:10.1371/journal.pone.0113644.g005 PLOS ONE | DOI:10.1371/journal.pone.0113644 November 26, 2014 8 / 14 Backward Adjustable Thoracic Support Figure 6. The results of back muscle activation measurement. Comparison of mean maximal voluntary isometric contraction (MVIC) of the lumbar multifidus (LM), lumbar erector spinae (LES), iliocostalis lumborum pars thoracis (ICLT), and thoracic erector spinae at T9 (TES) across 4 sitting postures, which include the slumped (SS), normal (NS), lumbar support (LSS), and backward adjustable thoracic support (BTS) sitting postures. Left side indicate -L, Right side -R, Error bars indicate SD, and * indicates p,0.05. doi:10.1371/journal.pone.0113644.g006 and lumbar angle values (P,0.001). In contrast with the NS posture, the BTS posture appeared to yield significantly lower lumbar angle values (P,0.001), but no significant differences in pelvic angle were observed. The BTS posture appeared to yield significantly higher values for pelvic angle (P,0.001) and lower values for lumbar angle (P50.014) when compared with the LSS posture. No significant differences in thoracic angle were observed, except for the NS versus the BTS, The latter posture appeared to yield significantly higher values (P50.003). Back Muscle Activation The results of the back muscle activation measurements are shown in Figure 6. In contrast with the SS posture, the NS, LSS and BTS postures appeared to produce significantly more muscle activity in all the tested muscles (P,0.05). Compared with the NS posture, the LSS and BTS postures appeared to produce significantly less muscle activity in all the tested muscles (P,0.05). Compared with the LSS, BTS posture appeared to produce significantly less muscle activity in all the tested muscles (P,0.05). Discussion Choosing a suitable wheelchair seating system is essential for patients with lower limb disorders for improving postural support and decreasing the risk of complications during the rehabilitation phase or daily life. This study suggested a new sitting posture concept, which is the BTS posture. We also quantitatively investigated the biomechanical effects induced by the BTS posture and compared it with 3 common wheelchair sitting postures. The BTS posture was defined by a PLOS ONE | DOI:10.1371/journal.pone.0113644 November 26, 2014 9 / 14 Backward Adjustable Thoracic Support rather neutral pelvic tilt, high lumbar lordosis and low back muscle activation. Consequently, the results confirmed our hypothesis. Pelvic tilt may influence hamstring tightness [11, 12]. In this study, the SS posture presented the greatest posterior pelvic tilt among the 4 sitting postures, decreasing hamstring tightness. However, the posterior pelvic tilt increased the shear stress between the sacral spine and the seat, thereby increasing the risk of sacral pressure ulcers [30–32]. The LSS posture exhibited the greatest anterior pelvic tilt, increasing hamstring tightness. In addition, the muscles were tensed because of stretching, which increased the passive tension load of peripheral viscoelastic tissues and the mechanical microvascular resistance and reduced the capillary diameter, the blood flow, and the intracapillary red blood cell velocity [9, 33, 34]. These changes may influence the nutrition metabolism of surrounding tissues. A compromising and balanced method through the NS and the BTS postures could enable us to have a neutral pelvic tilt. Lumbar curvature could influence the stress on the intervertebral discs [9]. We found that the SS posture exhibited the greatest level of lumbar kyphosis among the 4 sitting postures. It could increase stress and metabolite accumulations on the intervertebral discs, causing disc degeneration and herniation [9, 35]. The NS posture appeared to generated a relatively flat lumbar curvature. Insufficient lordosis cannot effectively reduce the hydrostatic pressure in the nucleus pulposus of the intervertebral disc [9]. In addition, patients with flat lumbar may experience problems of nonfunctioning absorption mechanism [36]. Both the LSS and the BTS this outer surface is not a serous lined layer which is not capable of producing fluid. In everted sacs, the lined serous layer was in direct contact with the scrotal wall where lymphatics are able to drain fluid production. This evidence argues against primacy for the concept that transudate production/reabsorption problems represent the essence of the majority of chronic hydrocele fluid accumulation in lymphatic filariasis. Based on results of the current study, it seems reasonable to propose that, first, the straw colored ‘‘filarial hydrocele fluid’’ consists of a combination of clear lymph fluid and transudate, in various proportions. The major mechanism of chronic filarial hydrocele proposed in the present study, is the same for milky fluid accumulation in cases of chylocele. In chyloceles the difference is the presence of chylomicrons caused by diffuse and extensive high retroperitoneal lymphangiectasia promoting the retrograde flow of milky lymph in ruptured intrascrotal lymphatics (J. Noro˜es, personal communication). Second, based on G2 findings the high hydrocele recurrence rate in CG was likely to be due to the presence of lymphatic fistula in everted hydrocele sac and/or in surrounding tissue. Based on the current findings it is suggested that the term ‘‘filaricele’’ be introduced for chronic straw colored fluid accumulation in the vaginal cavity in endemic areas. This term would help to emphasize the differences in pathogenesis and in the recommended surgical techniques that are appropriate for acquired chronic filarial and non-filarial hydroceles. On the other hand, the term chylocele should be kept for the milky appearance of hydrocele fluid rich in chylomicrons. Two other practical lessons were also learned from this study: (1) in the second recurrent case from G1, the sac extended up to the spermatic cord, and a small posterior segment of the sac wall, adherent to the cord, was inadvertently not excised at the first hydrocelectomy. During the re-operation a small portion of tunica vaginalis in the inferior part of the cord was found to contain a small cystic hydrocele. Thus, excision of the tunica vaginalis should be as complete as possible; (2) in hydrocele among patients from non-endemic areas, the patient’s personal preference as to whether or not he desires treatment should be given strong consideration since the indication for treatment depends, particularly, upon how much the hydrocele bothers him. By contrast, chronic filarial hydrocele could threaten the integrity of the testis even in small volume cases as shown in this study. Thus the medical indication for surgical treatment is stronger and the patient should be advised accordingly. It was beyond of the scope of this study to compare the volume of all hydrocele cases, echogenicity of the fluid, spermogram profiles and microfilaraemia status, which are planned to be published separately. One potential limitation of the study was the small sample size of Group 2. In spite of that, this group provided unprecedented detailed findings leading to a pioneering classification of recurrent hydrocele in endemic area occurring after eversion technique with and without partial excision of the hydrocele sac. In conclusion, in bancroftian filariasis endemic areas, lymphatic fistulae are likely to be an important mechanism responsible for chronic hydrocele, whether recurrent or not. Particularly with the intent to avoid hydrocele recurrence and testicular damage, complete excision of the hydrocele sac with its dilated lymphatic vessels and/or lymphatic fistula is advised as is identification and suturing or excision of any visible dilated lymphatic vessels in surrounding tissue, whether leaking or not. Acknowledgments The authors thank the patients for their trust and valuable cooperation during the study, which made such long follow-up possible; Anders Seim and Patrick Lammie for review and helpful suggestions on the original manuscript; Anders Seim for having suggested the term ‘‘filaricele’’ in September 2003; Wendilynn McAfee for valuable help with literature retrieval and the residents in urology for their participation in the surgeries. Author Contributions Conceived and designed the experiments: JN GD. Performed the experiments: JN. Analyzed the data: JN GD. Contributed reagents/ materials/analysis tools: JN GD. Wrote the paper: JN GD. Operated on all patients enrolled in the study: JN. References 1. World Health Organization (2005) Global programme to eliminate lymphatic filariasis. Wkly Epidemiol Rec 80: 202–212. 2. Michael E, Bundy DAP, Grenfell BT (1996) Re-assessing the global prevalence and distribution of lymphatic filariasis. Parasitology 112(Pt 4): 409–428. 3. Thambugala RL (1971) The radical cure of hydrocele of the tunica vaginalis: the technique of excision of the sac. Brit J Surg 58: 517–518. 4. Gratama S (1969) The pathogenesis of hydrocele in filarial infection. Trop Geogr Med 21: 254–268. 5. Wijers DJB (1977) Bancroftian filariasis in Kenya. I. Prevalence survey among adult males in the coast province. Ann Trop Med Parasitol 71: 313–331. 6. Medeiros Z, Gomes J, Beliz F, Coutinho A, Dreyer P, et al. (1999) Screening of army soldiers for Wuchereria bancrofti infection in metropolitan Recife region, Brazil: implications for epidemiologic surveillance. Trop Med Int Health 4: 499–505. 7. Noro˜es J, Addiss D, Cedenho A, Figueredo-Silva J, Lima G, et al. (2003) Pathogenesis of filarial hydrocele: risk associated with intrascrotal nodules caused by death of adult Wuchereria bancrofti. Trans R Soc Trop Med Hyg 97: 561– 566. 8. Noro˜ es J, Addiss D, Santos A, Medeiros Z, Coutinho A, et al. (1996) Ultrasonographic evidence of abnormal lymphatic vessels in young men with adult Wuchereria bancrofti infection in the scrotal area. J Urol 156: 409–412. 9. Noro˜es J, Addiss D, Amaral F, Coutinho A, Medeiros Z, et al. (1996) Occurrence of living adult Wuchereria bancrofti in the scrotal area of men with microfilaraemia. Trans R Soc Trop Med Hyg 90: 55–56. 10. Dreyer G, Santos A, Noro˜ es J, Addiss D (1999) Proposed panel of diagnostic criteria, including the use of ultrasound, to refine the concept of ‘endemic normals’ in lymphatic filariasis. Trop Med Int Health 4: 575– 579. 11. Dreyer G, Noro˜es J, Figueredo-Silva J, Piessens WF (2000) Pathogenesis of lymphatic disease in bancroftian filariasis: a clinical perspective. Parasitol Today 16: 544–548. www.plosntds.org 8 June 2010 | Volume 4 | Issue 6 | e695 Hydrocele in Bancroftian Filariasis 12. Figueredo-Silva J, Noro˜es J, Cedenho A, Dreyer G (2002) The histopathology of bancroftian filariasis revisited: the role of the adult worm in the lymphatic-vessel disease. Ann Trop Med Parasitol 96: 531–541. 13. Dreyer G, Addiss D, Roberts J, Noro˜es J (2002) Progression of lymphatic vessel dilatation in the presence of living adult Wuchereria bancrofti. Trans R Soc Trop Med Hyg 96: 157–161. 14. Dreyer G, Addiss D, Santos A, Figueredo-Silva J, Noro˜es J (1998) Direct assessment in vivo of the efficacy of combined single-dose ivermectin and diethylcarbamazine against adult Wuchereria bancrofti. Trans R Soc Trop Med Hyg 92: 219–222. 15. Noro˜es J, Figueredo-Silva J, Dreyer G (2009) Intrascrotal nodules in adult men as a marker for filarial granuloma in a bancroftian filariasis-endemic area. Am J Trop Med Hyg 81: 317–321. 16. Dreyer G, Noro˜es J, Addiss D (1997) The silent burden of sexual disability associated with lymphatic filariasis. Acta Trop 63: 57–60. 17. Rinker JR, Allen L (1951) A lymphatic defect in hydrocele. Am Surg 17: 681–686. 18. Ozdilek S (1957) The pathogenesis of idiopathic hydrocele and a simple operative technique. J Urol 77: 282–284. 19. Rodriguez WC, Rodriguez DD, Fortun˜ o RF (1981) The operative treatment of hydrocele: a comparison of 4 basic techniques. J Urol 125: 804–805. 20. Gottesman JE (1976) Hydrocelectomy: evaluation of technique. Urology 7: 386–387. 21. Haas JA, Carrion HM, Sharkey J, Politano VA (1978) Operative treatment of hydrocele. Urology 12: 578–579. 22. Nigam VK (1984) Window operation: new technique for hydrocele. Urology 24: 481–482. 23. Albrecht W, Ho¨ltl W, Aharinejad S (1991) Lord’s procedure – the best operation for hydrocele? J Urol 68: 187–189. 24. Ku JH, Kim ME, Lee NK, Park YH (2001) The excisional, plication and internal drainage techniques: a comparison of the results for idiopathic hydrocele. BJU Int 87: 82–84. 25. Fasana F (1982) Treatment of tropical hydrocele: a study of 273 cases. Medicom 4: 73–75. 26. Thomas G, Richards Jr. FO, Eigege A, Dakum NK, Azzuwut MP, et al. (2009) A pilot program of mass surgery weeks for treatment of hydrocele due to lymphatic filariasis in Central Nigeria. Am J Trop Med Hyg 80: 447–451. 27. Mo¨ller R (1980) Arrangement and fine structure of lymphatic vessels in the human spermatic cord. Andrologia 12: 564–576. www.plosntds.org 9 June 2010 | Volume 4 | Issue 6 | e695
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