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Hindawi Publishing Corporation ISRN Electrochemistry Volume 2013, Article ID 367872, 9 pages http://dx.doi.org/10.1155/2013/367872 Research Article An Immunosensor for Pathogenic Staphylococcus aureus Based on Antibody Modified Aminophenyl-Au Electrode Amani Chrouda, 1,2 Mohamed Braiek, 1 Karima Bekir Rokbani, 3 Amina Bakhrouf, 3 Abderrazak Maaref, 2 and Nicole Jaffrezic-Renault 1 1 Institute of Analytical Sciences, University of Lyon, UMR CNRS 5280, 5 rue de la Doua, 69100 Villeurbanne, France 2 Laboratory of Interfaces and Advanced Materials, Faculty of Sciences, University of Monastir, Avenue de l’Environnement, 5019 Monastir, Tunisia 3 Laboratory of Analysis, Treatment and Valorisation of Pollutants of Environment and of Products, Faculty of Pharmacy, University of Monastir, 5019 Monastir, Tunisia Correspondence should be addressed to Nicole Jaffrezic-Renault; nicole.jaff[email protected] Received 8 August 2013; Accepted 9 September 2013 Academic Editors: S. Arya and E. M. Richter Copyright © 2013 Amani Chrouda et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. e objective of this work is to elaborate an immunosensing system which will detect and quantify Staphylococcus aureus bacteria. A gold electrode was modified by electrograſting of 4-nitrophenyl diazonium, in situ synthesized in acidic aqueous solution. e immunosensor was fabricated by immobilizing affinity-purified polyclonal anti S. aureus antibodies on the modified gold electrode. Cyclic voltammetry (CV) and Faradaic Electrochemical Impedance Spectroscopy (EIS) were employed to characterize the stepwise assembly of the immunosensor. e performance of the developed immunosensor was evaluated by monitoring the electron-transfer resistance detected using Faradaic EIS. e experimental results indicated a linear relationship between the relative variation of the electron transfer resistance and the logarithmic value of S. aureus concentration, with a slope of 0.40 ± 0.08 per decade of concentration. A low quantification limit of 10 ± 2 CFU per ml and a linear range up to 10 7 ± 2 × 10 6 CFU per mL were obtained. e developed immunosensors showed high selectivity to Escherichia coli and Staphylococcus saprophyticus. 1. Introduction Staphylococcus aureus is a major human pathogen respon- sible for a broad range of diseases because it is able to produce heat-resistant toxins in food [1]. Foods that are frequently incriminated in staphylococcal poisoning include meat and meat products, milk, and water. e toxic chemical released by S. aureus is enterotoxin that has been found to be produced at a hazardous level for 10 8 cells per kg of food [2]. erefore rapid, sensitive, and reliable methods to detect foodborne pathogens are increasingly necessary in health care today. Traditional methods for foodborne bacteria detection including polymerase chain reaction (PCR) [3], enzyme-linked immunosorbent assay [4], and those based on culture and colony counting [5] have been widely applied due to their high reliability. However, these methods suffer from obvious disadvantages: they are time consuming and require expensive equipment and complicated pretreatment, so they are difficult to use on site. Biosensor technologies play an increasingly important role in the detection of pathogenic bacteria because they present the great potential of satisfying the practical need for rapid, wearable, and low-cost detection [6]. Among biosensors, immunosensors are widely investigated for bac- teria detection due to their specific advantages, such as high affinity and simple fabrication [6, 7]. In the literature, many recent studies focus on E. coli and Salmonella bacteria detection with different transducing techniques: QCM [8], SPR [9], electrochemical techniques: capacitive [10] and amperometric measurements [11]. Although several electro- chemical immunosensors for the detection of foodborne pathogenic bacteria have been reported in the literature,

DIVIDENDS:(THE(TRADE(OFF(people.stern.nyu.edu/adamodar/pdfiles/acf4E/webcastslides/session… · DIVIDENDS:(THE(TRADE(OFF(“Companies(don’thave(cash.(They(hold(cash(for(their(stockholders.”(1!

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Page 1: DIVIDENDS:(THE(TRADE(OFF(people.stern.nyu.edu/adamodar/pdfiles/acf4E/webcastslides/session… · DIVIDENDS:(THE(TRADE(OFF(“Companies(don’thave(cash.(They(hold(cash(for(their(stockholders.”(1!

DIVIDENDS:  THE  TRADE  OFF  “Companies  don’t  have  cash.  They  hold  cash  for  their  stockholders.”  

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The Investment DecisionInvest in assets that earn a return

greater than the minimum acceptable hurdle rate

The Financing DecisionFind the right kind of debt for your firm and the right mix of debt and

equity to fund your operations

The Dividend DecisionIf you cannot find investments that make your minimum acceptable rate, return the

cash to owners of your business

Hurdle Rate4. Define & Measure Risk5. The Risk free Rate6. Equity Risk Premiums7. Country Risk Premiums8. Regression Betas9. Beta Fundamentals10. Bottom-up Betas11. The "Right" Beta12. Debt: Measure & Cost13. Financing Weights

Investment Return14. Earnings and Cash flows15. Time Weighting Cash flows16. Loose Ends

Financing Mix17. The Trade off18. Cost of Capital Approach19. Cost of Capital: Follow up20. Cost of Capital: Wrap up21. Alternative Approaches22. Moving to the optimal

Financing Type23. The Right Financing

Dividend Policy24. Trends & Measures25. The trade off26. Assessment27. Action & Follow up28. The End Game

Valuation29. First steps30. Cash flows31. Growth32. Terminal Value33. To value per share34. The value of control35. Relative Valuation

Set Up and Objective1: What is corporate finance2: The Objective: Utopia and Let Down3: The Objective: Reality and Reaction

36. Closing Thoughts

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Three  Schools  Of  Thought  On  Dividends  

1.  If    there  are  no  tax  disadvantages  associated  with  dividends  &    companies  can  issue  stock,  at  no  issuance  cost,  to  raise  equity,  whenever  needed  

Dividends  do  not  ma-er,  and  dividend  policy  does  not  affect  value.  

2.  If  dividends  create  a  tax  disadvantage  for  investors  (relaMve  to  capital  gains)  

Dividends  are  bad,  and  increasing  dividends  will  reduce  value  3.   If  dividends  create  a  tax  advantage  for  investors  

(relaMve  to  capital  gains)  and/or  stockholders  like  dividends  

Dividends  are  good,  and  increasing  dividends  will  increase  value  

3

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The  Dividends  don’t  maQer  school  The  Miller  Modigliani  Hypothesis  

¨  The  Miller-­‐Modigliani  Hypothesis:  Dividends  do  not  affect  value  ¨  Basis:  

¤  If  a  firm's  investment  policies  (and  hence  cash  flows)  don't  change,  the  value  of  the  firm  cannot  change  as  it  changes  dividends.    

¤  If  a  firm  pays  more  in  dividends,  it  will  have  to  issue  new  equity  to  fund  the  same  projects.  By  doing  so,  it  will  reduce  expected  price  appreciaMon  on  the  stock  but  it  will  be  offset  by  a  higher  dividend  yield.  

¤  If  we  ignore  personal  taxes,  investors  have  to  be  indifferent  to  receiving  either  dividends  or  capital  gains.  

¨  Underlying  AssumpMons:  (a)  There  are  no  tax  differences  to  investors  between  dividends  and  capital  gains.  (b)  If  companies  pay  too  much  in  cash,  they  can  issue  new  stock,  with  no  flotaMon  costs  or  signaling  consequences,  to  replace  this  cash.  (c)  If  companies  pay  too  liQle  in  dividends,  they  do  not  use  the  excess  cash  for  bad  projects  or  acquisiMons.  

4

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II.  The  Dividends  are  “bad”  school:  And  the  evidence  to  back  them  up…  

0.00%  

10.00%  

20.00%  

30.00%  

40.00%  

50.00%  

60.00%  

70.00%  

80.00%  

90.00%  

100.00%  

1916 1918 1920 1922 1924 1926 1928 1930 1932 1934 1936 1938 1940 1942 1944 1946 1948 1950 1952 1954 1956 1958 1960 1962 1964 1966 1968 1970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2011 2013

 Tax  rates  on  dividends  and  capital  gains-­‐  US  

Dividend  tax  rate   Capital  gains  tax  rate  

5

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What  do  investors  in  your  stock  think  about  dividends?  Clues  on  the  ex-­‐dividend  day!  

¨  Assume  that  you  are  the  owner  of  a  stock  that  is  approaching  an  ex-­‐dividend  day  and  you  know  that  dollar  dividend  with  certainty.  In  addiMon,  assume  that  you  have  owned  the  stock  for  several  years.    

P  =  Price  at  which  you  bought  the  stock  a  “while”  back  Pb=  Price  before  the  stock  goes  ex-­‐dividend  Pa=Price  ajer  the  stock  goes  ex-­‐dividend  D  =  Dividends  declared  on  stock  to,  tcg  =  Taxes  paid  on  ordinary  income  and  capital  gains  respecMvely  

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Ex-dividend day

Dividend = $ D Initial buy At $P

Pb Pa

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Cashflows  from  Selling  around  Ex-­‐Dividend  Day  

¨  The  cash  flows  from  selling  before  ex-­‐dividend  day  are:  Pb  -­‐  (Pb  -­‐  P)  tcg    

¨  The  cash  flows  from  selling  ajer  ex-­‐dividend  day  are:  Pa  -­‐  (Pa  -­‐  P)  tcg  +  D(1-­‐to)  

¨  Since  the  average  investor  should  be  indifferent  between  selling  before  the  ex-­‐dividend  day  and  selling  ajer  the  ex-­‐dividend  day  -­‐  Pb  -­‐  (Pb  -­‐  P)  tcg  =  Pa  -­‐  (Pa  -­‐  P)  tcg  +  D(1-­‐to)  

¨  Some  basic  algebra  leads  us  to  the  following:  

7

Pb −PaD

=1− to1− tcg

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IntuiMve  ImplicaMons  

¨  The  relaMonship  between  the  price  change  on  the  ex-­‐dividend  day  and  the  dollar  dividend  will  be  determined  by  the  difference  between  the  tax  rate  on  dividends  and  the  tax  rate  on  capital  gains  for  the  typical  investor  in  the  stock.  

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Tax Rates Ex-dividend day behavior

If dividends and capital gains are taxed equally

Price change = Dividend

If dividends are taxed at a higher rate than capital gains

Price change < Dividend

If dividends are taxed at a lower rate than capital gains

Price change > Dividend

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The  empirical  evidence…  

•  Ordinary  tax  rate  =  70%  •  Capital  gains  rate  =  28%  •  Price  change  as  %  of  Dividend  =  78%  

1966-­‐1969  

•  Ordinary  tax  rate  =  50%  •  Capital  gains  rate  =  20%  •  Price  change  as  %  of  Dividend  =  85%  

1981-­‐1985  

•  Ordinary  tax  rate  =  28%  •  Capital  gains  rate  =  28%  •  Price  change  as  %  of  Dividend  =  90%  

1986-­‐1990  

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Two  bad  reasons  for  paying  dividends  1.  The  bird  in  the  hand  fallacy  

¨  Argument:  Dividends  now  are  more  certain  than  capital  gains  later.  Hence  dividends  are  more  valuable  than  capital  gains.  Stocks  that  pay  dividends  will  therefore  be  more  highly  valued  than  stocks  that  do  not.  

¨  Counter:  The  appropriate  comparison  should  be  between  dividends  today  and  price  appreciaMon  today.  The  stock  price  drops  on  the  ex-­‐dividend  day.  

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2.  We  have  excess  cash  this  year…  

¨  Argument:  The  firm  has  excess  cash  on  its  hands  this  year,  no  investment  projects  this  year  and  wants  to  give  the  money  back  to  stockholders.  

¨  Counter:  So  why  not  just  repurchase  stock?  If  this  is  a  one-­‐Mme  phenomenon,  the  firm  has  to  consider  future  financing  needs.      The  cost  of  raising  new  financing  in  future  years,  especially  by  issuing  new  equity,  can  be  staggering.  

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Three  “good”  reasons  for  paying  dividends…  

¨  Clientele  Effect:  The  investors  in  your  company  like  dividends.  

¨  The  Signalling  Story:  Dividends  can  be  signals  to  the  market  that  you  believe  that  you  have  good  cash  flow  prospects  in  the  future.  

¨  The  Wealth  AppropriaMon  Story:  Dividends  are  one  way  of  transferring  wealth  from  lenders  to  equity  investors  (this  is  good  for  equity  investors  but  bad  for  lenders)  

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I.  The  Clientele  Effect  

¨  Basis:  Investors  may  form  clienteles  based  upon  their  tax  brackets.  Investors  in  high  tax  brackets  may  invest  in  stocks  which  do  not  pay  dividends  and  those  in  low  tax  brackets  may  invest  in  dividend  paying  stocks.    

¨  Evidence:  A  study  of  914  investors'  pormolios  was  carried  out  to  see  if  their  pormolio  posiMons  were  affected  by  their  tax  brackets.  The  study  found  that    ¤  (a)  Older  investors  were  more  likely  to  hold  high  dividend  stocks  and  

¤  (b)  Poorer  investors  tended  to  hold  high  dividend  stocks  

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2.  Dividends  send  a  signal”  Increases  in  dividends  are  good  news..  

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But  higher  or  new  dividends  may  signal  bad  news  (not  good)  

0.00%  

5.00%  

10.00%  

15.00%  

20.00%  

25.00%  

30.00%  

35.00%  

40.00%  

45.00%  

-­‐4   -­‐3   -­‐2   -­‐1   1   2   3   4  

Annu

al  Earnings  G

rowth  Rate  

Year  rela@ve  to  dividend  ini@a@on  (Before  and  aDer)  

Dividend  Ini@a@ons  and  Earnings  Growth  

15

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Both  dividend  increases  and  decreases  are  becoming  less  informaMve…  

-­‐6.00%  

-­‐5.00%  

-­‐4.00%  

-­‐3.00%  

-­‐2.00%  

-­‐1.00%  

0.00%  

1.00%  

1962-­‐1974   1975-­‐1987   1988-­‐2000  

Market Reaction to Dividend Changes over time: US companies

Dividend  Increases  

Dividend  Decreases  

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3.  Dividend  increases  may  be  good  for  stocks…  but  bad  for  bonds..  

-2!

-1.5!

-1!

-0.5!

0!

0.5!

t:-!15!

-12! -9! -6! -3! 0! 3! 6! 9! 12! 15!

CAR (Div Up)!

CAR (Div down)!

EXCESS RETURNS ON STOCKS AND BONDS AROUND DIVIDEND CHANGES!

Day (0: Announcement date)!

CAR!

Bond price drops

Stock price rises

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What  managers  believe  about  dividends…  18

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Read  Chapter  10  Task  

Examine  the  trade  offs  on  whether  your  

company  should  be  paying  more  

or  less  in  dividends.