Re: intro chapter on logic

[Brian Whatcott <inet@INTELLISYS.NET>]

At 05:56 PM 12/30/01, Joe Heafner wrote:
> Good Evening.
>
> In our introductory physics and astronomy courses, we very often speak of
> teaching our students how to think critically and how to employ valid
> scientific reasoning.
...
> This idea came to me last week while reading the first chapters of Jeff
> Bennett and William Briggs' text "Using and Understanding Mathematics: A
> Quantitative Reasoning Approach, Second Edition" published by
> Addison-Wesley. It suddenly occurred to me that we can never expect our
> students to learn this stuff unless authors actually include it in their
> texts and we, the instructors, actually include it in our classes.
>
>
> Cheers,
> Joe


I have had some exposure to a sort of Harvard case study method which
reviews the experimental protocols offered by authors of research papers
 in a field, with the task of providing critical appraisals of their approach.

This seems to lead in the general direction to which Joe refers.
And here's a benefit: you could apply this approach over a range of
student levels.

The topic came up when I was browsing a newsgroup
for (boat) cruising. There is a lively interest in minimizing fuel tank
contamination. Discussion turned to a magnetic gadget intended to
 reduce loading of fuel filters for diesel engines.
Someone included the following text of a student project.
See if you can find the effective field strength.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
JOURNAL OF EXPEDITIOUSLY  RESEARCHED  MICROBIOLOGY 1997

Electromagnetic Effects on the Growth of Escherichia coli K12 Charles J.
Bright and Kathleen E. Davidson St. Mary's College of Maryland, St.
Mary's, Maryland Revised 07 May 1997 and accepted

The growth of Escherichia coli K12 was investigated after exposure to a
magnetic field created by a
wire coil and a power converter. The bacteria was suspended in a test
tube in the center of the magnetic field.
The duration of the exposure and voltage were varied. The bacterial
growth rate was significantly decreased
as measured by the initial rates of the growth curves. The initial cell
concentration was also adversely
affected in correlation to the voltages of the electromagnet.

INTRODUCTION
Controlling microbial growth is an important health and economic concern
in today's society. Some of today's major health concerns, such as food
poisoning, have been linked to microbial causes. Rising health costs and
governmental regulations have made the control of these microorganisms a
priority and have led to extensive research in this field. Ecological
concerns have also influenced researchers to find alternative methods of
microbial control that do not add toxic and hazardous chemicals to the
environment.
Several researchers focused their studies on the effects of
electromagnetism on the growth of microorganisms. Bacteria were exposed
to high frequency electromagnetic fields for as long as 14 days while in
another study low frequency fields were used (1, 3). Results have shown
that growth rates appear to decline when organisms are exposed to
varying electromagnetic fields (1). One idea suggested for this
occurrence is that the phospholipid membrane electrical gradient created
in the cell is disrupted. Under normal circumstances, the cell maintains
a net negative charge on the internal side of the phospholipid membrane.
The flux may alter this gradient to a point beyond which the cell is
able to correct, and the membrane will be torn apart (2). In this
experiment, the bacteria Escherichia coli K12 was exposed to different
electromagnet fields in the attempt to control its growth. Figure 1
-Magnetic Coil Apparatus used to expose E. coli to an electromagnetic
field. The test tube was suspended in the center of the coil using a
wooden plate. Wood was used to avoid electrical conduction.

MATERIALS AND METHODS
Bacteria. A sample of E. coli K12 (St. Mary's College of Maryland) was
obtained and grown on a TSA (Difco Laboratories) slant. A bacterial
stock culture was cultivated in 250ml of sterile TSB (Difco
Laboratories) in an Erlenmeyer flask and incubated for 24 hours in a 37
q C shaking water bath prior to magnetic exposure. Electromagnet. The
magnet was formed by running a current from a power generator through a
coil measuring 6" L
x 2. 25" Dia of 12 gauge wire (fig. 1). The coil contained two complete
cycles of the wire over its entire length 3 3 Page 4 5 Media. Tryptic
Soy Broth ( Di fco Labor at or i es ) was prepared according to
instructions and used in preparation of the bacterial stock culture and
as a growth medium after magnetic exposure. Tryptic Soy Agar (Difco
Laboratories) was DISCUSSION prepared according to instructions and used
as a growth medium for the plate counts. Saline dilution tubes (9. 0ml,
9. 9ml) were of the E. coli. The electromagnet appears to be affecting
the prepared using 7. 5g of NaCl per liter of RO water. reproduction of
the bacteria in some manner. All media was autoclaved for 20 mins at 121
q F at 15psi. Magnetic Exposure and Growth
Measurement. A 3ml sample of stock culture E. coli in a test tube was
suspended within the magnetic coil (fig.
1) according to the times and voltages in Table 1. A 1ml sample of the
'magnetized' bacteria was re-suspended in 75ml of TSB and incubated at
37 q C. Bacterial growth curves were developed by conducting plate
counts every 30mins for 2hr. The plates were incubated for 24hrs at 37 q
C and the colony forming units counted. Absorbance readings of a 3ml
sample were conducted every 15mins at 520nm using a spectrometer. A
control growth curve was conducted by using a 'non-magnetized' bacteria,
stock culture not exposed to the magnetic field..
Table 1 -Electromagnetic Treatments
Voltage Time( mins)
25          15, 30
50          15, 30
75          15, 30

RESULTS
In both the 15 and 30 minutes exposure times, the absorbance readings of
the samples over the 2hrs were lower than the control (fig. 2 and 3).
The electromagnet appeared to have the most effect on the bacteria in
the first 45mins after exposure. The absorbance reading of the treated
bacteria decreased or showed only a very small increase after 15 minutes
of growth (fig. 4 and 5). The initial growth rates were calculated as
the slope of the best fit line for each voltage/ exposure time (fig, 6).
The first four absorbance readings (0, 15, 30, 45 mins), before growth
reached the exponential phase, were used to form the best fit line.
Colony forming units were counted and compared to absorbance to ensure
that the absorbance readings were viable cells as opposed to dead cell
debris. The slopes of the logarithmic functions of absorbency and colony
forming units were similar in all treatments when 3 extraneous data
points were removed (fig. 7). Points were removed because of the extreme
discrepancy between the plate counts of the two trials at a particular
voltage/ time treatment. The large number of colony forming units on
these plates indicated a dilution or pipetting error. The initial rates
indicate that the treatment of 50 volts for 30 minutes had most profound
effect on the initial growth The exposure to 75 volt electromagnet
appears to be killing the cells more readily than the lower voltages
since the absorbance appears to be reading the viable cell count (fig 8
and 9). But the initial rate at the 75 volt treatments are both higher
then the 50 volt/ 30 minute treatment. This leads to the conclusion that
the higher voltage may be killing the bacterial cells. The lower voltage
does not appear to be killing the cells but in some way temporarily
disabling their reproduction and growth. The electromagnetic effects on
the bacteria only appear to last for a short period of time. The 25 volt
exposures exhibits the longest effect over time. This is indicated by
the lower slope of the logarithmic function of the absorbance (fig. 8,
9, and 10). The results of this experiment do not draw a clear
conclusion of the electromagnetic effects on E. coli. Further research
needs to be conducted to conclude what the actual metabolic effects of
the electromagnet is having on the bacteria. In other words, the
mechanism by which the electromagnet is causing the detrimental affect
on E. coli needs to be determined.

ACKNOWLEDGMENTS
We would like to thank Jennifer Mullendore and Kristina Tucker for their
laboratory assistance and Dr. Teymour Darkhosh (Physics Dept., St.
Mary's College) for the use of the physics laboratory equipment.

LITERATURE CITED
1. Alexander, M. P. 1996. Effect of VHF and high-amplitude alternating
EMF on the growth of bacteria. Electro and Magnetobiology. 15( 1):
57-62.
2. McGeechan, F. X. 1996. Controlling microorganism in Diesel Fuel... A
New Solution to an Old Problem. Proceedings of the Marine Safety
Council. 27( 3): 28-30.
3. Tsuchiya, K., Nakamure, K., Okuno, K., Ano, T. And Shoda, M. 1996.
Effect of homogeneous and inhomogeneous high magnetic fields and the
growth of Escherichia coli. J. of Fermentation and Bioengineering. 81(
4):
-----------------------------------
<snip>
source:
<http://www.nsm.smcm.edu/Biology/bio_journals/jerm1997.pdf>

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~




Brian W
Brian Whatcott
  Altus OK                      Eureka!