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Copyright © 2012, Campbell R. Harvey. All Rights Reserved.

Half Life

In a pool of mortgages underlying a mortgage-backed security, the length of time it takes for half the aggregate principal to be repaid. A half life is normally about 12 years, but this may vary depending on how often homeowners refinance their mortgages (which pays off all principal at once). Half lives are calculated for mortgage-backed securities issued or guaranteed by Freddie Mac, Fannie Mae, and Ginnie Mae.

Weighted Average Life

The amount of time for the principal on a loan or a mortgage to be paid off. The length of the weighted average life depends on the amount of principal paydowns and how often they are made. Once the WAL is calculated, one can determine how long it will take to pay off half of the remaining principal.
Farlex Financial Dictionary. © 2012 Farlex, Inc. All Rights Reserved


The length of time before half the principal on a debt is expected to be repaid through amortization or sinking fund payments. For example, a 25-year bond issue may require the issuer to retire 5% of the beginning principal commencing 5 years after the issue date. Thus, the bond issue has a half-life of 5 years plus the number of years required to retire half the issue, or 15 years. Mortgage-backed securities often have a relatively short half-life because many homeowners pay off or refinance their mortgages early. Also called average life.
Wall Street Words: An A to Z Guide to Investment Terms for Today's Investor by David L. Scott. Copyright © 2003 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved. All rights reserved.
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The molecular weight of the free base (about 428) and the long mean plasma half-lives of the parent drug and active metabolite (57 and 200 hours) suggest that the drug will cross the placenta.
We differentiate between two categories of POPs: a) POPs whose intrinsic elimination half-lives ([t.sup.elim.sub.1/2]) are shorter than their intake doubling times ([t.sup.in.sub.2]) and intake half-lives ([t.sup.in.sub.1/2]) (e.g., BDE-47), and b) POPs whose [t.sup.elim.sub.1/2] values are longer than [t.sup.in.sub.2] and [t.sup.in.sub.1/2] (e.g., PCB-153).
[10] recently constructed novel EPO derivatives with prolonged half-live times by adding peptides to the carboxyl terminus of EPO without using linkers.
The only deficiency in the experiment is the slightly larger error between theoretical and experimental half-lives.
By binding to the patient's serum albumin the half-life of the therapeutic compound is dramatically enhanced, meaning that drugs with natural half-lives of minutes can be converted into AlbudAb-drug conjugates with half-lives well over a week.
So it may be that at least some of the nucleosides are essential in maintaining long-term suppression after you stop the medications, in a way that is perhaps beyond half-lives. Maybe these drugs interfere with rebound alter interruption in a way that we don't understand yet.
The overall half-life is determined--in the case of some of these agents by active metabolites that have lengthy half-lives, which in turn, can be associated with long-lasting daytime sedation.
As a benchmark for comparison to the preliminary results, consider the half-lives estimated for international deviations from LOP (that is, from Purchasing Power Parity) by Frankel and Rose [JIE, February 1996] who found a half-life of 4.6 years, a result that has been corroborated by several authors.
Both have pretty short half-lives." I advised that online newsletter writing must be even more succinct than print newsletter writing and that online writing should be concrete, graphic, and gripping.
On the x-axis, plot the number of half-lives, and on the y-axis, undecayed atoms.
The half-lives were derived individually from the slope of the line of best fit calculated by linear regression analysis of the logarithm of the concentration remaining against the time of incubation.
The half-lives of the [H.sub.6]RI[alpha] (3.3hours) and [H.sub.6]RI[[alpha].sub.S81A] (3.8hours) proteins do not appear to be different, suggesting that phosphorylation is not influencing the half-life of RI[alpha].