Heavy Relative of the Neutron Discovered

Once produced, the neutral Xi-sub-b (Symbol for Xi-sub-b) particle travels about a millimeter before it disintegrates into two particles: the short-lived, positively charged Xi-sub-c (Symbol Xi-sub-c^+) and a long-lived, negative pion (À-). The Xi-sub-c then promptly decays into a pair of long-lived pions and a Xi particle (Symbol pi^-), which lives long enough to leave a track in the silicon vertex system (SVX) of the CDF detector before it decays a pion and a Lambda (›). The Lambda particle, which has no electric charge, can travel several centimetres before decaying into a proton (p) and a pion (À). (Credit: CDF collaboration)

Science Daily  — Scientists of the CDF collaboration at the Department of Energy's Fermi National Accelerator Laboratory announced the observation of a new particle, the neutral Xi-sub-b (Ξ_b⁰). This particle contains three quarks: a strange quark, an up quark and a bottom quark (s-u-b). While its existence was predicted by the Standard Model, the observation of the neutral Xi-sub-b is significant because it strengthens our understanding of how quarks form matter.

The neutral Xi-sub-b is the latest entry in the periodic table of baryons. Baryons are particles formed of three quarks, the most common examples being the proton (two up quarks and a down quark) and the neutron (two down quarks and an up quark). The neutral Xi-sub-b belongs to the family of bottom baryons, which are about six times heavier than the proton and neutron because they all contain a heavy bottom quark. The particles are produced only in high-energy collisions, and are rare and very difficult to observe.Fermilab physicist Pat Lukens, a member of the CDF collaboration, presented the discovery at Fermilab on July 20, 2011.

Although Fermilab's Tevatron particle collider is not a dedicated bottom quark factory, sophisticated particle detectors and trillions of proton-antiproton collisions have made it a haven for discovering and studying almost all of the known bottom baryons. Experiments at the Tevatron discovered the Sigma-sub-b baryons (Σ_b and Σ_b*) in 2006, observed the Xi-b-minus baryon (Ξ_b^-) in 2007, and found the Omega-sub-b (Ω_b^-) in 2009. The lightest bottom baryon, the Lambda-sub-b (Λ_b), was discovered at CERN. Measuring the properties of all these particles allows scientists to test and improve models of how quarks interact at close distances via the strong nuclear force, as explained by the theory of quantum chromodynamics (QCD). Scientists at Fermilab and other DOE national laboratories use powerful computers to simulate quark interactions and understand the properties of particles composed of quarks.

Once produced, the neutral Xi-sub-b travels a fraction of a millimeter before it decays into lighter particles. These particles then decay again into even lighter particles. Physicists rely on the details of this series of decays to identify the initial particle. The complex decay pattern of the neutral Xi-sub-b has made the observation of this particle significantly more challenging than that of its charged sibling (Ξ_b^-). Combing through almost 500 trillion proton-antiproton collisions produced by Fermilab's Tevatron particle collider, the CDF collaboration isolated 25 examples in which the particles emerging from a collision revealed the distinctive signature of the neutral Xi-sub-b. The analysis established the discovery at a level of 7 sigma. Scientists consider 5 sigma the threshold for discoveries.

CDF also re-observed the already known charged version of the neutral Xi-sub-b in a never before observed decay, which served as an independent cross-check of the analysis. The newly analyzed data samples offer possibilities for further discoveries.

The CDF collaboration submitted a paper that summarizes the details of its Xi-sub-b discovery to the journal Physical Review Letters. It will be available on the arXiv preprint server on July 20, 2011.

CDF is an international experiment of about 500 physicists from 58 institutions in 15 countries. It is supported by the U.S. Department of Energy, the National Science Foundation and a number of international funding agencies.

Fermilab is a national laboratory funded by the Office of Science of the U.S. Department of Energy, operated under contract by Fermi Research Alliance, LLC.

Sperm Coat Protein May Be Key to Male Infertility

Science Daily  — The loss of a protein that coats sperm may explain a significant proportion of infertility in men worldwide, according to a study by an international team of researchers led by UC Davis. The research could open up new ways to screen and treat couples for infertility.

Gary Cherry, a professor at the UC Davis Bodega Marine Laboratory and Center for Health and Environment, and Cherr, the senior author of the paper, said the protein DEFB126 acts as a "cloaking device," allowing sperm to swim through mucus and avoid the immune system to reach the egg. The paper describing the work was published on July 20 in the journal Science Translational Medicine.

However, the UC Davis researchers found that many men carry a defective gene for DEFB126. A survey of samples from the U.S., United Kingdom and China showed that as many as a quarter of men worldwide carry two copies of the defective gene -- which may significantly affect their fertility.

Infertility affects 10 to 15 per cent of the U.S. population, said John Gould, associate professor of urology at UC Davis, who was not involved in the research. About half of those cases involve problems with male fertility.

One of the mysteries of human fertility is that sperm quality and quantity seem to have little to do with whether or not a man is fertile, said Ted Tollner, first author of the paper, who carried out the work as a postdoctoral scholar with Cherry. Tollner is now an adjunct assistant professor in the UC Davis Department of Obstetrics and Gynecology.

"In 70 per cent of men, you can't explain their infertility on the basis of sperm count and quality," Cherry said. Gould said that studies like this may give us opportunities to explain these cases.

If the discovery were successfully developed into a test, it could be used to send couples directly to treatment with intracytoplasmic sperm injection or ICSI, in which eggs are removed from the woman and injected directly with sperm, avoiding an expensive workup to exclude other causes, Gould said.

Tollner and Cherr were looking for ways to make contraceptive vaccines when they started looking at DEFB126. The protein belongs to a class of molecules called defensins, natural germ-killers found on mucosal surfaces. DEFB126 is produced in the epididymis, the structure where sperm are stored after they are produced in the testes, and deposited onto sperm in the epididymis to form a thick coat.

Tollner and Cherr were trying to make antibodies to the human protein, without much success. So they enlisted the help of Professor Charles Bevins, an expert on defensins who had just joined the UC Davis Department of Medical Microbiology and Immunology.

Bevins' lab made a recombinant copy of the human DEFB126 gene, with the aim of generating a purified protein that Tollner and Cherr could use to create antibodies. On their first attempt, they found the gene had a mutation that prevented it from making a protein. But when they used sperm from a different donor, they were able to make the normal protein.

"If we hadn't seen this in the first clone, we would be confused to this day," Bevins said.

Sperm from men with the defective DEFB126 genes look normal under a microscope and swim around like normal sperm. But they are far less able to swim through an artificial gel made to resemble human cervical mucus.

When the normal protein is added to the sperm, they recover their normal abilities, the team found.

Working with Edward Hollox at the University of Leicester, England, Xiping Xu at the University of Illinois, Chicago, and Scott Venners at Simon Fraser University, Canada, the researchers were able to look at the frequency of the gene in DNA samples from people in the U.S., United Kingdom, China, Japan and Africa.

They found that worldwide, about half of all men carry one defective copy; a quarter have two defective copies and therefore make sperm that are poor at swimming through mucus.

In collaboration with Xue Liu and other scientists at Anhui Medical University in Anhui, China, the epidemiology team headed by Venners was able to look at the effect of the mutation on a group of couples trying to conceive. They found a statistically significant decrease in the number of pregnancies in couples where the man carried two copies of the defective DEFB126 gene.

Why should a mutation that affects fertility be so astonishingly common? It may be that heterozygotes -- men with one normal and one defective gene, but normal fertility -- are advantaged in some way, Tollner said.

Tollner noted that compared to sperm from monkeys and other mammals, human sperm are typically poor quality, slow-swimming, and with a high rate of defective cells. It's possible that because humans, unlike most mammals, breed in long-term monogamous relationships, sperm quality just does not matter very much, Cherr said.

However, some researchers believe that, for reasons unknown, human male fertility has been falling worldwide in recent decades. That decline might be unmasking the problems associated with the defective DEFB126 gene.

Cherr said that they hope next to work with a major infertility program in the U.S. to further explore the role of the mutation.

Other authors of the paper are: Ashley Yudin and James Overstreet, Center for Health and Environment, and Robert Kays, Tsang Lau, Department of Medical Microbiology and Immunology, UC Davis; and Genfu Tang and Houxun Xing, Anhui Medical University.

The study was funded by grants from the National Science Foundation and the National Institutes of Health.

Researchers Identify Seventh and Eighth Bases of DNA

The newly discovered seventh and eighth bases of DNA -- called 5-formylcytosine and 5 carboxylcytosine -- are actually versions of cytosine that have been modified by Tet proteins, molecular entities thought to play a role in DNA demethylation and stem cell reprogramming. (Credit: © Rodolfo Clix / Fotolia)

Science Daily  — For decades, scientists have known that DNA consists of four basic units -- adenine, guanine, thymine and cytosine. Those four bases have been taught in science textbooks and have formed the basis of the growing knowledge regarding how genes code for life. Yet in recent history, scientists have expanded that list from four to six.

These last two bases -- called 5-formylcytosine and 5 carboxylcytosine -- are actually versions of cytosine that have been modified by Tet proteins, molecular entities thought to play a role in DNA demethylation and stem cell reprogramming.Now, with a finding published online in the July 21, 2011, issue of the journal Science, researchers from the UNC School of Medicine have discovered the seventh and eighth bases of DNA.

Thus, the discovery could advance stem cell research by giving a glimpse into the DNA changes -- such as the removal of chemical groups through demethylation -- that could reprogram adult cells to make them act like stem cells.

"Before we can grasp the magnitude of this discovery, we have to figure out the function of these new bases," said senior study author Yi Zhang, Ph.D., Kenan Distinguished Professor of biochemistry and biophysics at UNC and an Investigator of the Howard Hughes Medical Institute. "Because these bases represent an intermediate state in the demethylation process, they could be important for cell fate reprogramming and cancer, both of which involve DNA demethylation."

Much is known about the "fifth base," 5-methylcytosine, which arises when a chemical tag or methyl group is tacked onto a cytosine. This methylation is associated with gene silencing, as it causes the DNA's double helix to fold even tighter upon itself.

Last year, Zhang's group reported that Tet proteins can convert 5 methylC (the fifth base) to 5 hydroxymethylC (the sixth base) in the first of a four step reaction leading back to bare-boned cytosine. But try as they might, the researchers could not continue the reaction on to the seventh and eighth bases, called 5 formylC and 5 carboxyC.

The problem, they eventually found, was not that Tet wasn't taking that second and third step, it was that their experimental assay wasn't sensitive enough to detect it. Once they realized the limitations of the assay, they redesigned it and were in fact able to detect the two newest bases of DNA. The researchers then examined embryonic stem cells as well as mouse organs and found that both bases can be detected in genomic DNA.

The finding could have important implications for stem cell research, as it could provide researchers with new tools to erase previous methylation patterns to reprogram adult cells.

It could also inform cancer research, as it could give scientists the opportunity to reactivate tumor suppressor genes that had been silenced by DNA methylation.

The research was funded by the Howard Hughes Medical Institute and the National Institutes of Health.

Study co-authors from UNC include Shinsuke Ito, Ph.D.; Li Shen, Ph.D.; Susan C. Wu, Ph.D.; Leonard B. Collins and James A. Swenberg, Ph.D

Exoplanet Aurora: An Out-Of-This-World Sight

This artist's conception shows a "hot Jupiter" and its two hypothetical moons with a sunlike star in the background. The planet is cloaked in brilliant aurorae triggered by the impact of a coronal mass ejection. Theoretical calculations suggest that those aurorae could be 100-1000 times brighter than Earth's. (Credit: David A. Aguilar (CfA))

ScienceDaily ) — Earth's aurorae, or Northern and Southern Lights, provide a dazzling light show to people living in the polar regions. Shimmering curtains of green and red undulate across the sky like a living thing. New research shows that aurorae on distant "hot Jupiters" could be 100-1000 times brighter than Earthly aurorae. They also would ripple from equator to poles (due to the planet's proximity to any stellar eruptions), treating the entire planet to an otherworldly spectacle.

"I'd love to get a reservation on a tour to see these aurorae!" said lead author Ofer Cohen, a SHINE-NSF postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics (CfA).

Earth's aurorae are created when energetic particles from the Sun slam into our planet's magnetic field. The field guides solar particles toward the poles, where they smash into Earth's atmosphere, causing air molecules to glow like a neon sign. The same process can occur on planets orbiting distant stars, known as exoplanets.

Particularly strong aurorae result when Earth is hit by a coronal mass ejection or CME -- a gigantic blast that sends billions of tons of solar plasma (electrically charged, hot gas) into the solar system. A CME can disrupt Earth's magnetosphere -- the bubble of space protected by Earth's magnetic field -- causing a geomagnetic storm. In 1989, a CME hit Earth with such force that the resulting geomagnetic storm blacked out huge regions of Quebec.

Cohen and his colleagues used computer models to study what would happen if a gas giant in a close orbit, just a few million miles from its star, were hit by a stellar eruption. He wanted to learn the effect on the exoplanet's atmosphere and surrounding magnetosphere.

The alien gas giant would be subjected to extreme forces. In our solar system, a CME spreads out as it travels through space, so it's more diffuse once it reaches us. A "hot Jupiter" would feel a stronger and more focused blast, like the difference between being 100 miles from an erupting volcano or one mile away.

"The impact to the exoplanet would be completely different than what we see in our solar system, and much more violent," said co-author Vinay Kashyap of CfA.

In the model, a CME hits the "hot Jupiter" and weakens its magnetic shield. Then CME particles reach the gas giant's atmosphere. Its aurora lights up in a ring around the equator, 100-1000 times more energetic than Earthly aurorae. Over the course of about 6 hours, the aurora then ripples up and down toward the planet's north and south poles before gradually fading away.

Despite the extreme forces involved, the exoplanet's magnetic field shields its atmosphere from erosion.

"Our calculations show how well the planet's protective mechanism works," explained Cohen. "Even a planet with a magnetic field much weaker than Jupiter's would stay relatively safe."

This work has important implications for the habitability of rocky worlds orbiting distant stars. Since red dwarf stars are the most common stars in our galaxy, astronomers have suggested focusing on them in the search for Earthlike worlds.

However since a red dwarf is cooler than our Sun, a rocky planet would have to orbit very close to the star to be warm enough for liquid water. There, it would be subjected to the sort of violent stellar eruptions Cohen and his colleagues studied. Their future work will examine whether rocky worlds could shield themselves from such eruptions.

This research has been accepted for publication in The Astrophysical Journal and is available online.

Parasites Help Reveal New Ecological Rules: Animal Species Large and Small Follow Same Rule for How Common They Are in Ecosystems

This parasitic isopod, which is related to rolley pollies, is one of the larger parasites encountered by the researchers in the estuaries. The isopod is almost one centimeter long, and was found infecting a crab, which it had "parasitically castrated," completely blocking the host's reproduction. (Credit: Ryan Hechinger)

Science Daily — Scientists at UC Santa Barbara and other institutions say their new research is expected to profoundly affect the field of ecology and can assist the management of ecosystems, including forests, lakes, and oceans. And it's all because of parasites.

The research, published this week in the journal Science, includes parasites in a comprehensive study of ecosystems. By doing so, the scientists say they have revealed new ecological rules.

"The major finding of our research is that all types of animals -- parasites or otherwise -- appear to follow exactly the same rule for how common they are," said Ryan Hechinger, lead author and associate research biologist with the Marine Science Institute at UCSB.

"This includes birds, fishes, insects, crabs, clams, and all the parasites that live inside and on them," said Hechinger. "They all seem to follow the same rule. And the rule is simple. You can predict how common an animal is just by knowing how big an individual is and how high in the food chain it is."

Hechinger explained that body size is important because it determines how much food an animal needs. A given amount of food supports fewer big animals than small animals because each big animal needs more food. The food chain is important because the higher an animal is in the food chain, the less food there is and, therefore, the less common that species is.

According to the scientists, they did something no one has previously done: They went into an ecosystem and paid attention to parasites, treating them as equal players with other animals. "We realized that despite being small, parasites feed high up the food chain and might break the rule that smaller animals are more common," said co-author Kevin Lafferty, ecologist with the U.S. Geological Survey at UCSB.

The data were collected at three estuaries in Southern California and Baja California. The researchers counted and weighed parasites and other animals before documenting that parasites were indeed less common than other small animals.

"Paying attention to parasites was central to the study," said co-author Armand Kuris, professor of zoology at UCSB. "Parasites are at least half of all biodiversity. And they are different in some very basic ways than other life forms. However, ecological science usually ignores them. How can we possibly understand how life works if we don't look at half of the species -- the parasites?

"Considering parasites helped us find the right theory, see the true patterns in nature, and better test the theory," Kuris said. "In addition to body size, the general rule for animal abundance must factor in the food chain and let both small and large animals be top consumers."

The scientists also discovered a second general rule: that the amount of biomass produced by a population does not depend on the body size of the animals in the population, or on what type of animal -- bird, fish, crab, or parasite.

"If this rule is general, it means an aphid population can produce the same amount of biomass as a deer population," said Lafferty. "Furthermore, tapeworms that feed on the deer population produce less biomass than the deer, but can produce the same as a mountain lion population that also feeds on the deer."

"Predicting animal abundance is one of the most basic and useful things ecological science can provide for management and basic research," said Hechinger. "This simple rule helps with that because it may apply to all life forms and can easily be applied to complex ecosystems in the real world."

Additional co-authors include Andy Dobson of Princeton University and the Santa Fe Institute, and James Brown of the University of New Mexico.

The research was partly funded by the joint National Science Foundation-National Institutes of Health's Ecology of Infectious Diseases program.

Lists of Civil and Structural Engineering Books

these are the lists of books/articles i have downloaded from different sites...stored in discs and some in my pc...

rapidshare, 4shared, gigapedia and others..
pdf files

1. 1997 Uniform Building Code Structural Engineering Design Provisions
2. 1997 Uniform Building Code v2
3. ACI Structural Engineering Handbook 04 Structural Concrete Design
4. ACI318M - 2005
5. ACI318R - 2005
6. ACI-318R-08 Building Code Requirements for Structural Concrete and Commentary
7. Acoustic Detailing for Multi-storey Residential Buildings
8. Advanced Earthquake Engineering Analysis
9. AISC - Load and Resistance Factor Design
10. Aluminium Design and Construction
11. Analysis of Reinforced Concrete Floor Slabs for Storm Shelters
12. Architectural Detailing - Function, Constructibility, Aesthetics
13. Architectural Structures
14. Architecture Design Notebook
15. ASCE 7-05 Minimum Design Loads for Buildings and Other Structures
16. Assessing Building Performance
17. Basic Coastal Engineering
18. Basic Tools of Reinforced Concrete Beam Design
19. Bridge and Structural Design
20. Bridge Design Manual
21. Bridge Desk Analysis
22. Bridge Engineering Seismic Design
23. BS - Part 1-1984 Design Loading for Buildings
24. BS 2573-1-1983
25. BS 2573-2-1980
26. BS 7608-1993
27. Build Your Own Smart Home
28. Building Code Requirements for Structural Concrete
29. Building Construction Glossary
30. Building Construction Handbook
31. Building Design and Construction Handbook
32. Building Systems for Interior Designers
33. Civil Engineering Formulas
34. Civil Engineering Hydraulics
35. Code Check - Building
36. Code of Practice for the Structural Use of Steel
37. Code of Standard Practice for Steel Buildings and Bridge 2005
38. Complete Buildings and Projects
39. Composite Structures - Design, Safety and Innovation
40. Composite Structures of Steel and Concrete - Volume I
41. Computer-Aided Materials Selection During Structural Design
42. Concrete
43. Concrete Culverts and Conduits
44. Concrete Formwork Systems
45. Concrete Slabs
46. Concrete Slabs Designed With Fem
47. Conduits, Culverts and Pipes
48. Construction Building Envelope and Interior Finishes Databook
49. Construction of Buildings 1, 3-5
50. Construction of Marine and Offshore Structures
51. Daylighting - Natural Light in Architecture
52. Design for Construction
53. Design for Construction - SCI
54. Design of Concrete Masonry Diaphragm Walls - CST
55. Design of Earthquake Resistance Buildings
56. Design of Masonry Structures
57. Design of Pile Foundation
58. Design of Wood Structures ASD
59. Design with Structural Steel - A Guide for Architects
60. DG 10 Erection Bracing of Low-Rise Steel Buildings
61. DG 13 Stiffening of Wide Flange Columns
62. Dictionary of Engineering
63. DIY - Home Plumbing Repair
64. Ductility Reinforcement for Flat Slabs in Seismic Areas
65. Durability of Light Steel Framing in Residential Building - SCI
66. Earthquake Engineering for Concrete Dams
67. EC6 Design of Masonry Structures
68. Economic Concrete Frame Elements
69. Elementary Structural Analysis
70. Encyclopedia of 20th-Century Architecture A-F
71. Encyclopedia of Materials, Parts, and Finishes
72. Engineering Companion
73. Engineering Problem Solving - A Classical Perspective
74. Evaluation of Earthquake Damaged Concrete and Masonry Wall Buildings
75. Fluid Mechanics
76. Frontiers of Engineering
77. Geotech Design Guidelines for Building On liquefiable Sites
78. Guide to Earthwork Construction
79. Handbook of Structural Engineering
80. Hydraulics in Civil and Environmental Engineering
81. International Building Code 2006
82. International Plumbing Code
83. Lighting Modern Buildings
84. Manual for Design of Reinforced Concrete Building Structures to EC2
85. Manual for the Design of Plain Masonry In Building Structure
86. Manual for the Design of Reinforced Concrete Building Structure
87. Manual for the Design of Steelwork Building Structures to EC3
88. Manual of Engineering Drawing
89. Manual of Soil Analysis
90. Marine Structural Design
91. Masonry - Instant Answers Handbook
92. Masonry and Concrete for Residential Construction
93. Mechanics of Structural Elements
94. Metal Building Systems - Design and Specifications
95. New Seismic Design Provisions in Japan
96. Non-conventional Concrete Technologies Renewal of the Highway Infrastracture 
97. Notes on Design of Steel Parking Structures Including Seismic Effects
98. Outstanding Wood Buildings
99. Outstanding Wood Buildings - CWC
100. Philosophy and Design - From Engineering to Architecture
101. Planning the Modern Public Library Building
102. Plumbing - Water Supply -Sprinkler and Wastewater Systems
103. Post Tensioned Concrete Floors
104. Practical Foundation Engineering
105. Preventing Earthquake Disasters
106. Project Planning, Scheduling and Control
107. Recommended Seismic Design Criteria for New Steel Moment Frame Buildings
108. Refraction Seismology
109. Reinforced Concrete Analysis and Design
110. Reinforced Concrete Deep Beams
111. Reinforced Concrete Design to BS8110
112. Reinforced Soil Engineering - Advanced in Research and Practice
113. Reservoir Engineering Handbook
114. Residential Structural Design Guide
115. Safety and Health for Engineers
116. Safety at Work
117. Seismic Behavior and Design of Steel Shear Walls
118. Seismic Code Requirements
119. Seismic Conceptual Design of Buildings
120. Seismic Design of Buckling-Restrained Braced Frames
121. Seismic Provisions for Structural Steel Buildings
122. Seismic Rehabilitation of Buildings
123. Seismic Vulnerability of Flat Slab Structures
124. Soil & Foundation Manual 
125. Soil Mechanics
126. Soils and Geology Procedures for Foundation Design of Buildings
127. Soil-Structure Interaction for Footing Foundations
128. Specification for Structural Steel Building 2005
129. Stability of Buildings
130. Standard Method of Detailing Structural Concrete
131. Steel Buildings
132. Steel Columns and Struts
133. Structural Analysis
134. Structural Analysis for Performance- based Earthquake Engineering
135. Structural Details in Concrete
136. Structural Elements Design Manual
137. Structural Steel Designer's Handbook
138. Structural Steelwork Connections
139. Sustainable Building Technical Manual
140. Testing of Concrete in Structures
141. The Architect's Portable Handbook
142. The Civil Engineering Handbook
143. The Science and Engineering of Materials
144. What Designers Know
145. Wood Frame Const Details WCD1-300
146. Working Drawings Handbook
147. Shock, Impact and Explosion
148. Examples in Design Analysis
149. Design of Prestressed structures

CHM Files

1. Encyclopedia of Architectural and Engineering Feats

DJVU Files

1. 100 More of the World's Best Houses
2. Fundamentals of Earthquake Prediction
3. Stability of Structures
4. An Introduction to Geotechnical Engineering
5. Apartment Buildings - New Concepts

folder files

1. BEAMS AND COLUMNS
2. Doc & Dwg Template
3. DQR Steel Standard dwgs
4. Drawing
5. MS 1008 Storm water and drainage Earthwork
6. PANELLED BEAMS
7. Rectangular Beam Design
8. Seismic Design of Reinforced and Precast Concrete Buildings
9. Structural and Stress Analysis, Second Edition
10. Structural Steel Designer's Handbook
11. TrussMaster by Colin Caprani

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esteves101
manila, philippines

aval paranthu ponaley