There are many different types of ships cruising through the oceans. Among them are fishing trawlers, used to not only catch fish but also to process and refrigerate sea food at suitable temperatures.

It is not an easy feat to drag large trawls or fish nets and haul the load overboard and then to process it and refrigerate while sailing through tempestuous waters. The refrigeration systems of these ships need to be suitable for freezing large quantity of fish for long periods. These ships are designed in such a way that the load is distributed quite uniformly. So in order to place a refrigeration plant and `cargo holds` to store fish, it is made sure that this distribution of load is not disturbed too much, as concentrating heavy loads on a small portion would result in severe instability of the ship.

The fish are `filled` in containers which are stacked in the cargo holds in such a way that there are spaces between these individual stacks for cold air to circulate through. These stacks are fixed in place with the help of horizontal separators which prevent these stacks from colliding with each other and evaporator coils when the ship rolls. If these stacks get in physical contact with the cooling coils they would overcool and freeze, which is highly undesirable. This type of freezing can be observed even in domestic refrigerators when a jar placed too close to the evaporator coils freezes.

The insulating material used for the cargo holds should not only have small thermal conductivity but should also be water-resistant. In many insulation materials, air pockets are used. In fact, these air pockets impart insulating properties to an insulation material. If moisture is absorbed by the insulation material it would lose its insulation capability. This is why it happens the thermal conductivity of air is just 0.024 W/m.K at zero degree Celsius, while that of water and ice is 0.569 and 1.88 w/m.Krespectively, at the same temperature. This means that 77 per cent increase in thermal conductivity would occur when air gaps are replaced with ice.

There are three methods of cooling the storage holds direct cooling, air cooling and brine cooling. In direct cooling, the cooling coils are located within the cargo holds. A refrigerant is pumped into these coils which evaporates and absorbs heat from the hold. Only non-toxic refrigerants can be used in this system.

Brine is simply a solution of salt and water, and helps in lowering the freezing point of the mixture below zero degree Celsius. In brine cooling, refrigerants like ammonia cool brine is circulated through the coils in the cargo hold. These two cooling methods involve natural convection while in air cooling, the air is blown over the brine or refrigerant coils in cargo holds. That is, air cooling works on forced convection. It increases the rate of cooling and dehydration of the product, which ultimately affects the taste of fish and also decreases its weight.

Direct cooling is the most economical method because it uses only one refrigerant which means less piping and equipment need to be employed, resulting in low maintenance costs in contrast to brine cooling which involves two refrigerant loops.

It is interesting to note here that special care is taken when ammonia refrigeration systems are used because ammonia is very toxic, even a little leakage could result in disaster. Rooms that house ammonia refrigeration plants are ventilated much more liberally than those housing Freon refrigeration plants. Sprinklers are also provided and the exits are equipped with emergency continuous water curtains which can dissolve ammonia in case of a leakage.      

Long lasting results

Dr Mirza Shehab Afzal Beg, a highly trained plastic surgeon associated with Advance Hair Transplant & Cosmetic Surgery, a centre hair for restoration services, talks about issues related to hair transplantation.

Why is hair at the back of the head permanent?

This is a simple observation that men who have lost all hair at the front still retain hair at the back till very advanced age. So if these hairs are shifted to the front from the back, they are recognised by the system as earlier and hence they last forever.

Can this be explained scientifically?

Each hair has a root which has the capability to form and grow hair. The root is a complex structure which has many sensitive areas on it called receptors. Each receptor responds to specific hormones in the system and reacts accordingly. For example the male hormone (testosterone) acts on the receptors and starts a chemical process in the root which ultimately leads to hair fall. These receptors are not present in the hair at the back and therefore they do not fall.

Is hair transplant permanent?

Yes, this is a procedure where the results last for a lifetime.

Can women have this procedure too?

Yes, they can benefit from this too.

Is this a painful procedure?

Certainly not, people normally watch their favourite channel on the TV or read a book while this is being done. They also have sandwiches and juices during the procedure and are very relaxed.

How many hair can be transplanted in each session?

Anything between 6000 to 12000, depending upon the density of the donor site and elasticity of the scalp.

How many sessions can an individual have?

Depending on the width of the donor site, the sessions can be from two to four.

Can diabetic patients or people with high blood pressure have this procedure?

Sure, without any problems, provided their blood sugar and blood pressure are well under control.