or by postsynthesis treatments ( 28, 29). By contrast, separations such as H2/C3H8 that involve a
fast-permeating species are not appreciably affected by membrane defects. IMMP is also inherently a modular and parallel approach that
should allow independent and simultaneous processing of membranes in multiple fibers. To test
this hypothesis, we applied IMMP to the simultaneous processing of three hollow fibers. The total
bore flow rate was increased by a factor of 3 so
that the flow rate through individual fibers was
maintained. The ends of the module were capped
with PDMS, as described earlier. Figure 3, C and
D, shows that the H2/C3H8 and C3H6/C3H8
separation behavior is essentially identical to the
single-fiber case, demonstrating the potential for
scalability of IMMP. Given the overall importance
of tunable ZIF materials for a range of hydrocarbon and light-gas separations, the membrane-processing approach reported here overcomes
many limitations of current processes and is a
notable step toward realizing scalable molecular
sieving MOF membranes.
REFERENCES AND NOTES
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This work was supported by Phillips 66 Company. S.N., A.J.B.,
and C. W.J. conceived the research. A.J.B. and N.A.B. designed
the synthesis reactor. Hollow-fiber fabrication was carried out
by J.R.J. and W.J.K. Membrane synthesis, characterization, and
permeation measurements were carried out by A.J.B., K.E., and
F.R. Permeation modeling was carried out by S.N. and A.J.B.
All authors contributed to manuscript writing and editing. We thank
W. Qiu, R. P. Lively, and A. Rownaghi (all at Georgia Institute of
Technology) for helpful discussions. The Supplementary Materials
includes a detailed description of materials and methods, details
of the IMMP reactor, time-dependent flow profiles and synthesis
cases, SEM images of ZIF- 8 membranes, XRD patterns of
membranes, schematics of permeation apparatus and gas bypass
effects, EDX mapping of the ZIF- 8 membrane, permeation
modeling equations, and gas permeation data. A patent application
related to this work has been filed [U.S. patent application
61/820,489, filed 7 May 2013; S. Nair et al., Flow processing
and characterization of metal-organic framework (MOF)
membranes in tubular and hollow fiber modules].
Materials and Methods
Figs. S1 to S11
Tables S1 to S4
22 January 2014; accepted 19 May 2014
Just think: The challenges of the
Timothy D. Wilson,1 David A. Reinhard,1 Erin C. Westgate,1 Daniel T. Gilbert,2
Nicole Ellerbeck,1 Cheryl Hahn,1 Casey L. Brown,1 Adi Shaked1
In 11 studies, we found that participants typically did not enjoy spending 6 to 15 minutes in
a room by themselves with nothing to do but think, that they enjoyed doing mundane
external activities much more, and that many preferred to administer electric shocks to
themselves instead of being left alone with their thoughts. Most people seem to prefer to
be doing something rather than nothing, even if that something is negative.
“The mind is its own place, and in it self/
Can make a Heav'n of Hell, a Hell of Heav'n.”
– John Milton, Paradise Lost
The ability to engage in directed conscious thought is an integral part—perhaps even a defining part—of what makes us human. Unique among the species, we have the abil- ity to sit and mentally detach ourselves from
our surroundings and travel inward, recalling
the past, envisioning the future, and imagining
worlds that have never existed. Neural activity
during such inward-directed thought, called
default-mode processing, has been the focus of a
great deal of attention in recent years, and researchers have speculated about its possible
functions (1– 5). Two related questions, however, have been overlooked: Do people choose to
put themselves in default mode by disengaging
from the external world? And when they are in
this mode, is it a pleasing experience?
Recent survey results suggest that the answer
to the first question is “not very often.” Ninety-five percent of American adults reported that
they did at least one leisure activity in the past
24 hours, such as watching television, socializing, or reading for pleasure, but 83% reported
they spent no time whatsoever “relaxing or thinking” ( 6). Is this because people do not enjoy having
nothing to do but think?
Almost all previous research on daydream-
ing and mind wandering has focused on task-
unrelated thought, namely cases in which people
are trying to attend to an external task (such as
reading a book), but their minds wander invol-
untarily ( 7, 8). In such cases, people tend to be
happier when their minds are engaged in what
they are doing, instead of having wandered away
( 9, 10). A case could be made that it is easier for
people to steer their thoughts in pleasant direc-
tions when the external world is not competing
for their attention. We suggest, to the contrary,
that it is surprisingly difficult to think in enjoy-
able ways even in the absence of competing ex-
To address these questions, we conducted
studies in which college-student participants
spent time by themselves in an unadorned room
(for 6 to 15 min, depending on the study) after
storing all of their belongings, including cell
phones and writing implements. They were typically asked to spend the time entertaining themselves with their thoughts, with the only rules
being that they should remain in their seats and
stay awake. After this “thinking period,” participants answered questions about how enjoyable
the experience was, how hard it was to concentrate, etc.
Table 1 summarizes the results of six studies
that followed this procedure. Most participants
reported that it was difficult to concentrate
( 57.5% responded at or above the midpoint of
the point scale) and that their mind wandered
( 89.0% responded at or above the midpoint of
the scale), even though there was nothing competing for their attention. And on average, participants did not enjoy the experience very much:
49.3% reported enjoyment that was at or below
the midpoint of the scale.
1Department of Psychology, University of Virginia,
Charlottesville, VA, USA. 2Department of Psychology,
Harvard University, Cambridge, MA, USA.
*Corresponding author. E-mail: email@example.com