Mechanical Forage

Profitability of Grazing Versus Mechanical Forage Harvesting on New York Dairy Farms

The profitability of rotational grazing versus mechanical harvesting of forages was estimated using data from 237 nongrazing and 57 grazing farms participating in the New York farm business summary program in the year 2000. The objective was to perform an empirical comparison of the profitability of grazing versus mechanical forage harvesting systems. A regression analysis technique that controls for treatment selection bias is used to determine the impact of grazing on the rate of return on assets. This is accomplished by joint maximum likelihood estimation of a probit adoption function and a profit function. The results indicate that treatment selection does not have an important impact on the estimate of the profitability of grazing. There were wide ranges and overlap of profitability among herds using the two systems. However, other things equal, farmers utilizing grazing systems were at least if not more profitable than farmers not using grazing systems. After controlling for the factors influencing the decision to graze, we found that herd size, rate of milk production per cow, and prices received for milk have a strong positive impact on profitability. Farmers who perceive potential lifestyle benefits that might be obtained by implementing a grazing system likely do not have to pay an income penalty for adopting a grazing system.

The mechanical basis for airway hyperreactivity

New perspectives on the mechanical basis for airway hyperreactivity and airway hypersensitivity in asthma 

We revisit the airway wall model of Lambert et. al. (Lambert RK, Wiggs BR, Kuwano K, Hogg JC, and Pare PD. J Appl Physiol 74: 2771–2781, 1993). We examine in detail the notion of a general airway bistability such that the airway lumen can suddenly decrease from a relatively open to a relatively closed condition without needing additional increase in active airway smooth muscle (ASM) tension during the stimulation. The onset of this bistability is an emergent consequence of the balance of forces associated with airway wall properties, parenchymal tissue properties, maximum lung elastic recoil, and the maximum stress that the ASM can generate. In healthy lungs, we find that all these properties reside in conditions that largely prevent the emergence of the bistability even during maximum ASM stimulation. In asthmatic airways, however, the airway wall and ASM remodeling conditions can tip the balance so as to promote the onset of the bistability at a lower dose of ASM stimulation (enhanced sensitivity) and then work to amplify the maximum constriction reached by each airway (enhanced reactivity). Hence, a larger fraction of asthmatic airways can display overall airway hyperreactivity. Simulations studies examine the role of increasing ASM maximum tension, airway wall stiffening, reduced lung volume, and decreased parenchymal tethering. Results predict that the single most important factor causing this airway hyperreactivity is amplified maximum ASM tension and not a thickening of the airway wall per se.

airway walls; airway remodeling

 

MECHANICAL FACTORS

1. The lymph of the thoracic duct furnishes to the blood a larger proportion than is usually supposed of the lymphocytes in circulation. Gross variations in its output of such cells must affect very considerably the blood picture.

2. The quantity of lymphocytes supplied through the thoracic duct of the healthy dog remains practically constant from hour to hour, if the physiological conditions are not notably changed. Transient change in physiological conditions may alter the output of cells, but with the disappearance of this change the output tends to resume its previous rate. These facts indicate that the tissues producing lymphocytes are "set" at a rate of activity definite in the individual.

3. Muscular activity (struggle) produces a prompt increase in the output of lymphocytes through the thoracic duct.

(a) This is assured by the presence of an increased number of cells per cubic millimeter of lymph, combined with an increase in the amount of lymph voided.

(b) The lymphocyte-output may be tripled or quadrupled during a long-continued struggle.

(c) Following prolonged struggle the output of lymphocytes is for a short time less than previous to the exertion.

4. The increased lymph-flow caused by a lymphagogue of the second class (glucose) brings with it increased output of lymphocytes through the thoracic duct.

(a) The individual cubic millimeters of lymph are often poor in cells, during the rapid lymph-flow, yet the total number of elements transported is large.

(b) The results with glucose support the theory of Ehrlich, that a rapidly appearing lymphocytosis may be produced through the flushing effect of increased lymph-flow.

5. A comparison of the effects of struggle with those of glucose demonstrates that in the former some factor besides increase in lymph-flow per se (Ehrlich) works to cause the large output of lymphocytes. The nature of this factor has not yet been determined.

6. The variations caused by muscular exertion and by increased lymph-flow in the number of lymphocytes coursing through the thoracic duct are so pronounced as to suggest that the total number of lymphocytes in circulation must be considerably influenced by them. Clinical findings by other observers indicate that this is true; and the clinical findings themselves become much simpler of interpretation.

7. The results in general prove the existence, reserved from circulation, of a large fund of lymphocytes, which is quickly yielded to the blood under certain physiological conditions

Probe into poison boiler

A CHARITY has called for tighter regulation of the heating industry after two Arnold pensioners suffered carbon monoxide poisoning despite their boiler being checked by engineers.

Tenants Derek Cookson, 77, along with wife Joyce, 79, of Danes Close, were exposed to deadly fumes after repeated calls to Gedling Homes about the boiler being broken.

Mrs Cookson was rushed to hospital and Mr Cookson was left on the verge of collapse.

Now Gedling Homes has brought in an independent surveyor who is investigating the cause of the leak, alongside the Health & Safety Executive.

The charity National CO-Gas Safety had yesterday called for an independent investigation.

Stephanie Trotter president and director of CO-Gas Safety, said they have been monitoring the couple's situation since they read their story in the Evening Post.

The charity has campaigned for increased awareness about the threat of carbon monoxide poisoning since 1995.

Only CORGI engineers are allowed to work on gas appliances by law. No similar rules exist for those who have solid fuel burners, like the one in the Cooksons' home.

Mrs Trotter said: "We have always lobbied that solid fuel engineers should be registered by law."

On November 29, records left by an engineer who visited the Cooksons stated he was not trained to deal with solid fuel burners. Their daughter, Carole had already explained what type of boiler her parents had.

Jim Lambeth, general manager of advisory service, The Solid Fuel Association, said: "From the pictures I have seen the boiler is clearly in a poor state and vital maintenance has not been carried out.

"In any rented property, it's the responsibility of the landlord to maintain the boiler to keep it in working order and it's the tenant's responsibility to carry out routine maintenance.

"HETAS are a group who hold a list of approved solid fuel engineers but effectively anyone can be employed to service a solid fuel boiler. That's the problem, a council can employ anyone legally to do the job."

Lynne Clayton, managing director at Gedling Homes, said: "We are working hard to get Mr and Mrs Cookson back to their home. Specialist contractors are working today to ensure they can return safely which will be before the weekend. Temporary heating and hot water are in place. With Mr Cookson's agreement, a gas meter is being installed, and we will put in a new central heating system."

Mr Cookson, an ex-miner, used anthracite to fuel his boiler. A hard, compact variety of mineral coal, it can leave a residue in the flue of a boiler and if this is not properly maintained, it can lead to a blockage and fume leaks containing carbon monoxide

Control of cell membrane tension by myosin-I

Abstract

All cell functions that involve membrane deformation or a change in cell shape (e.g., endocytosis, exocytosis, cell motility, and cytokinesis) are regulated by membrane tension. While molecular contacts between the plasma membrane and the underlying actin cytoskeleton are known to make significant contributions to membrane tension, little is known about the molecules that mediate these interactions. We used an optical trap to directly probe the molecular determinants of membrane tension in isolated organelles and in living cells. Here, we show that class I myosins, a family of membrane-binding, actin-based motor proteins, mediate membrane/cytoskeleton adhesion and thus, make major contributions to membrane tension. These studies show that class I myosins directly control the mechanical properties of the cell membrane; they also position these motor proteins as master regulators of cellular events involving membrane deformation.

Post-Tensioning Revisited

Post-tensioned concrete has been used for more than 40 years in the United States in a wide variety of construction projects. First used primarily in bridge construction, applications for post-tensioning now extend far beyond bridges to include tanks, office buildings, condominiums, hotels, parking structures, pavement, masonry, seismic walls, single-family homes and more. Because post-tensioning can be combined effectively with other structural materials and has been used to strengthen steel, reinforced concrete, masonry and timber structures, as well as enhance and extend the capabilities of precast, pre-tensioned elements- the method's usage will continue to increase.
One reason for the increasing use of post-tensioning is the advancement in technology in recent years. While older post-tensioning systems focused more on obtaining the desired prestress force and less on durability, by improving the systems used to protect the prestressed steel from corrosion, the industry can now offer systems that deliver both. The advancements in corrosion protection are especially important in areas that experience significant exposure and damage from freeze-thaw cycles, de-icing salts, seawater, salt spray and other deterioration mechanisms.
Post-Tensioning Vs. Pre-Tensioning
Both pre-tensioning and post-tensioning systems are used to create prestressed concrete. Pre-tensioned systems, however, must be fabricated in a precast plant and are limited to straight, harped or circular tendons. This method is also limited to straight or circular members. Because pre-tensioning is used only in precast elements, it is more difficult to construct continuous structures because of the necessary connections. Additionally, though the tendons in pre-tensioned concrete are protected from corrosion because they are in direct contact with concrete, the steel itself is not able to be encapsulated in any other manner. As such, any moisture migrating to the steel through cracks in the concrete could cause the tendons to corrode.
Post-tensioning, on the other hand, can be performed on the project site or in a precast yard. Post-tensioning tendons can be configured into almost any shape. This flexibility allows the post-tensioning to match exact design requirements with few limitations. And, depending on project needs, the tendons in a post-tensioned system can be unbonded or bonded. For corrosion protection, whether unbonded or bonded - post-tensioning has superior features
Unbonded and Bonded Post-Tensioning Systems
Unbonded tendons typically consist of single (mono) strands or threaded bars that remain unbonded to the surrounding concrete throughout their service life - giving them freedom to move locally relative to the structural member. The strands in unbonded monostrand systems are coated with specially formulated grease with an outer layer of seamless plastic extruded in one continuous operation to provide protection against corrosion. Depending on the application and the level of protection that is needed, the anchorages of unbonded monostrand systems may also be encapsulated. Unbonded monostrand systems are typically used in new construction for elevated slabs, slabs-on-grade, beams and transfer girders, joists, shear walls and mat foundations. Light and flexible, unbonded monostrand can be easily and rapidly installed - providing an economical solution.
Bonded post-tensioning systems are comprised of tendons from one to multiple strands (multistrand) or bars. For bonded systems the prestressing steel is encased in a corrugated metal or plastic duct. After the tendon is stressed, cementitious grout is injected into the duct to bond it to the surrounding concrete. In addition, the grout creates an alkaline environment which provides corrosion protection for the prestressing steel. An advanced duct system, PT-Plus^TM, encases the prestressing steel in a corrugated duct and plastic coupler system.
Bonded strand post-tensioning systems can range from a single strand to 55 or more strands in a single tendon, while the anchorage assembly consists of local zone confinement reinforcement, bearing plate, anchor head, wedges and grout cap. Bonded multistrand systems, while used extensively in new construction of bridges and transportation structures, can be and have been successfully applied to commercial building structures. When these multistrand systems are used for large structural elements such as beams and transfer girders, design advantages include increased span lengths and load-carrying capacity and reduced deflection.
External and Internal Post-Tensioning
Tendons placed in the formwork prior to pouring the concrete are known as internal tendons. Most post-tensioning applications use internal tendons. In external applications, tendons are installed outside of the structural member. The system consists of prestressing steel, mechanical end anchorage devices and a corrosion protection system. External systems are generally installed in one of two configurations - either running straight between anchorages or through deviators to create harped profiles. The tendons are typically protected by high density polyethylene (HDPE) ducts filled with grout.
External systems, if designed accordingly, make it possible to control and adjust tendon forces, inspect for corrosion and, as necessary, easily replace the tendons. For these reasons, the primary application for external tendons is bridges where external multistrand systems are grouted in HDPE ducts. External tendon systems, however, can be applied to many types of structures and, in particular, provide effective strengthening reinforcement for retrofits.
Past Challenges Inspire Technological Advancement
Since post-tensioning was first used domestically, the industry has seen many technological advances. Improvements in systems include seven-wire strand with wedge-type anchorages, low relaxation strand and the use of banded tendons in flat plates. Analysis techniques and design software have advanced as have techniques for improving durability. These include extruded sheathing for unbonded tendons and encapsulated anchorages for enhanced corrosion resistance, plastic duct systems and the development of non-bleed grouts.
When some of the earliest unbonded post-tensioned buildings were about 15 years old, corrosion problems started to surface, and it was apparent that some of the tendon corrosion protection systems used could not adequately protect the tendons in the most aggressive environments, such as where de-icing salts are used or in coastal areas that have a high salt content in the air. Starting in the 1980s, the Post-Tensioning Institute (PTI) developed tendon specifications designed to address the corrosion problems. PTI specified improvements included sheathing, coatings and, in the most aggressive environments, complete encapsulation of the tendons.
With internal bonded and external tendons, grout is a key element of the overall corrosion protection strategy. Experience gained over many decades with grouted post-tensioning tendons has proven that cementitious grout provides excellent protection for the prestressing steel. The principle objectives of grouting are to protect the prestressing steel from corrosion by encasing it in a passive environment and filling the duct to minimize voids in the completed structure. To ensure the quality of grouting applications, and the ultimate durability of the structure, in addition to other training classes and certification programs, PTI developed and administers grout training classes and certification procedures. Specialized equipment has also been developed to complement the process and ensure the highest quality product.
Benefits of Post-Tensioned Concrete
Post-tensioned structures offer numerous advantages. These include reduced dead load and member depth because of the decreased amount concrete required. There is also increased deflection control and greater crack control. The improved crack control also improves durability which is another advantage. In addition to these advantages, post-tensioning allows for increased span to depth ratios. This advantage leads to lower building heights which in turn reduces the heating and cooling volume and decreases the façade area of the structure.
For developers and owners of commercial buildings, the advantages of post-tensioning can make it a preferred reinforcing system. "Since the slab thickness is reduced, a developer building a high rise structure can easily add more floors without increasing the overall building height," said Scott Greenhaus, president of VSL. "Over the course of the building's life, this can represent significantly increase leasing revenue for the owner."
A traditional reinforced concrete building with two-way slabs requires more concrete and thus, more weight. As a lighter alternative, post-tensioned slabs require less concrete to achieve the same performance, thereby creating a structure with fewer shear walls, smaller columns and lower foundation loads. This results in more durable, efficient structures with longer clear spans.
"For commercial building operators, residential developers and hotel operators, they can have more usable space within the building envelope," Greenhaus noted.
Further, in corrosive environments, encapsulated bonded systems offer significant design advantages that lead to life-cycle savings. Because the amount of mild steel is reduced, particularly at the top zone of slabs, there is less steel to corrode should the concrete crack or spall. This is particularly important in parking garages where significant maintenance costs are due to repairs associated with spalled concrete from corroded rebar. 
Another advantage of bonded post-tensioning is the inherent capacity to provide resistance to progressive collapse. This may be especially important in the event of localized blast loading. Like mild steel reinforcement, a bonded post-tensioning tendon is capable of developing its force in a relatively short distance along its length. In the event that an anchorage fails or a tendon is severed, the loss of tendon force would be localized. The remainder of the tendon would retain its force at the development length away from the failure point and would remain functional. This functionality can be considered in the design of a structure. 
Bonded post-tensioning systems also allow for flexibility when future modifications to the building are needed. Tenant build-outs, remodeling and changes in a building's use may require modifications to the floor slabs. The use of bonded post-tensioning systems has allowed owners the flexibility to make these changes quickly, easily and cost-efficiently.
An example of an owner choosing bonded post-tensioning for the method's life-cycle savings is the Baltimore Washington International Airport Consolidated Rental Facility. The bonded post-tensioning system used in this structure provides total encapsulation of the strands using PT Plus^TM plastic duct with watertight mechanical duct to anchorage couplers. The rental facility was completed in December 2003 and includes over one million square feet of elevated, post-tensioned, cast-in-place concrete.
Bonded and unbonded systems can be mixed within a structure. An example of how bonded and unbonded systems were combined for economics, efficiency and design requirements is the W Victory Hotel & Residences in Dallas, Texas. The W Victory's concrete frame structure includes a combination of monostrand, unbonded post-tensioning systems and bonded, multistrand post-tensioning systems. The unbonded post-tensioned systems were used in typical levels, while the bonded post-tensioning systems were specified for the transfer girders on three levels to provide optimum crack and deflection control --  features essential for transfer girders required to carry the loads from the multi-story structure. Additionally, bonded post-tensioning systems were used in exterior applications where corrosion could be an issue.
Post-tensioning has seen much development and many improvements over the past 50 years, resulting in the method now serving as a significant feature in mainstream construction. The next article in this series will review in-depth the contemporary uses of post-tensioning in building construction and how it can successfully be incorporated into a project design.
Reasons to Consider Post-Tensioning

• Increased span to depth ratio resulting in a reduction in construction materials and a subsequent reduction in overall cost.
  
  
• Positive deflection control.
  
  
• Designers are offered design flexibility with post-tensioning.
  
  
• Joints in structures are minimized or even eliminated.
  
  
• Post-tensioning can improve the long-term durability of concrete structures exposed to aggressive environments.
  
  
• Span lengths can be greatly increased.

Basic concepts in mechanical ventilation

Mechanical ventilatory support is a major component of the clinical management of critically ill patients admitted into intensive care. Closely linked with the developments within critical care medicine, the use of ventilatory support has been increasing since the polio epidemics in the 1950s (Lassen 1953). Initially used to provide controlled mandatory ventilation, today with advances in technology, most mechanical ventilators are triggered by the patient, increasing the awareness of the complexity of patient/ventilator interaction (Tobin 1994). Though ventilator appearance and design may have changed quite significantly and the variety of options for support extensive, the basic concepts of mechanical ventilatory support of the critically ill patient remains unchanged. This paper aims to outline these concepts so as to gain a better understanding of mechanical ventilatory support.