Format of Laboratory Writeups

Every writeup will have the format: Abstract, Introduction, Methods, Results, Discussion, Conclusion(s), References.

The abstract is a brief summary of the experiment. In general this will have one or two sentences for each one of the sections. An example is given below:

Experiments were carried out to determine the effect of stenosis length and severity on the pressure drop across a stenosis. Single stenoses were inserted in a section of tubing, and flow with Reynolds numbers from 200 to 1000 was imposed. Pressure was measured with a Statham model 27 transducer. A change in stenosis diameter reduction from 50% to 25% resulted in a significant reduction in the pressure loss (p = 0.0023), and a reduction in stenosis length from 2.54 cm to 1.27 cm also resulted in a smaller pressure loss (p = 0.11). A comparison between the data and Young’s equation for pressure loss across a stenosis showed similar trends, but the measured values were a factor of two higher than the theoretical values. The accuracy of the measurements was estimated to be ±5%. The stenosis shapes in these experiments differed from those used by Young. The data could be made to match a modified version of Young’s equation if the empirical constands were adjusted. The data suggest that an additional factor, such as stenosis shape or upstream flow conditions is affecting the pressure drop.

Notice that this abstract can be broken up as follows:

Introduction:

Experiments were carried out to determine what effect stenosis length and severity has on the pressure drop across a stenosis.

Methods:

Single stenoses were inserted in a section of tubing, and flow with Reynolds numbers from 200 to 1000 was imposed. Pressure was measured with a Statham model 27 transducer.

Results:

A change in stenosis diameter reduction from 50% to 25% resulted in a significant reduction in the pressure loss (p = 0.0023), and a reduction in stenosis length from 2.54 cm to 1.27 cm also resulted in a smaller pressure loss (p = 0.11). A comparison between the data and Young’s equation for pressure loss across a stenosis showed similar trends, but the measured values were a factor of two higher than the theoretical values.

Discussion:

The accuracy of the measurements was estimated to be ±5%. The stenosis shapes in these experiments differed from those used by Young. The data could be made to match a modified version of Young’s equation if the empirical constands were adjusted.

Conclusion:

The data suggest that an additional factor, such as stenosis shape or upstream flow conditions is affecting the pressure drop.

The main body of your report will then proceed as follows:

Introduction

State what you are going to do and why. In stating why, you must give some indication of the state of the art, i.e. what is known and what is not known about the phenomenon you are studying. However, you should not be giving a literature review here. You should give only enough information to tell the reader what your motivation is.

Methods

State how you did your measurements. This will usually require a diagram of the experimental setup, procedures for calibration, statement of what equipment was used (make and model number), description of the experimental protocol, and description of the statistical analysis.

Results

This will include plots of your data and a description of these plots. Any preliminary information, such as calibration curves and calibration coefficients should also be included here. Comments on calibrations (i.e. correlation coefficients for least squares fits, statement as to whether the calibration is linear) should also be made. All figures must be referenced in the text by figure number, and every figure must have a figure caption that describes the figure. You should make your figure captions self explanatory so that a casual reader of your report can get the general idea of your report merely by looking at your figures and reading their captions. Always use individual points to represent data values and lines to represent underlying models. For example, see Figure 1.

Notice that I have overridden the defaults of Excel in Figure 1. There is no excessive color in this plot. You do not want unnecessary color because not everyone has a color Xerox machine. I have also eliminated extra gridlines. The x and y axes contain both the variable being plotted and the units of that variable. Different data sets are distinguished by symbol shape, and not by color. The symbol sizes are 2 sizes larger than their default vaules for readability. Also notice that the theory for the entire span from 0 to 12 ml/s is plotted even though the data are shown for only 8 and 9 ml/s. Note also the use of the superscript and the Greek symbol D in the y-axis label. The superscript is obtained by highlighting the 2 on the axis label, right-clicking and selecting “Format Axis Title.” Select the font tab and then select the “superscript” box. Similarly, the Greek symbol is obtained by inserting a capital “D”, selecting the “D”, right clicking, selecting “Format Axis Title,” selecting the font tab, and then selecting the “symbol” font.

Finally, provide levels of significance for the statistical tests you have run. For example, for a T-test, what is the value of p?

Discussion

The discussion section will include interpretation of your experimental results. In some of the experiments this will be a matter of answering the questions provided. In others this section will be more open ended. You should consider the following:

1. What was the original question you set out to answer?
2. Is the experiment itself valid? Does it test the null hypothesis?
3. What systematic errors are there in the experiment?
4. What is a quantitative estimate of the error inherent in the data?
5. Do the results agree with what we already know about the system being studied?
6. What do you notice about the data that you did not anticipate in the original experimental design?
7. What new problems do the results raise?
8. What further experiments need to be done?

Question 1 is just a reiteration of what the state of the art looked like before you did this experiment. Questions 2-5 are designed to validate the correctness of the data and to let the reader know how much confidence he/she should have in the results. Questions 6-8 relate to the future of this line of investigation.

Conclusion

This is a reiteration of the main result you found in this study. It should relate to the problem statement in the introduction section, but you may wish to add additional caveats (e.g., The data match the theoretical analysis, but there is evidience that the system might be temperature senstitive as well).

References

Information that you cite from other journals should have a journal reference. Never include a reference unless you specifically refer to it in your text. For this course, use the following format:

Johnson, FJ, Samuels, JJ, Miller, BL, and Wang, T, “Measurements of pressure drops across non-symmetric stenoses,” Journal of Fluids Research, Vol. 14, pp. 222-230, 1999.

Acknowledgements

You may, in addition, have a section called “Acknowledgements,” in which you express thanks to those who have helped you, but who were not involved enough in the project to be a co-author. This is also where you acknowledge any funding received for the project.

Steven A. Jones

BIEN 435, Biomedical Senior Laboratory